Born and raised in Iowa, Kate is the daughter of diner worker Diane and Sam, a U.S. Army Ranger and Gulf War Veteran, who taught Kate to track deer in the wild during her childhood. At an early age she befriended Tom, and together they buried a time capsule beneath a large tree. Kate's parents later divorced, and Diane married an abusive alcoholic named Wayne. As an adult, Kate took out an insurance policy on her mother's home before blowing it up with Wayne inside, which she confessed to her mother before disappearing. Diane called the authorities, where Kate was arrested and handcuffed behind her back at a bus station by Edward Mars. As he drove her to be processed, a horse in the road caused him to lose control of the vehicle and crash, allowing Kate to escape. Kate then confronted Sam, realizing that he was in Korea at the time of her conception, and Sam revealed that Wayne was her biological father. Sickened by her relation to Wayne, Kate continued her fugitive lifestyle, but remained determined to learn why her mother surrendered her to the police. Under the alias of Lucy, she met an out-of-luck con artist named Cassidy Phillips, who helped her confront Diane in a diner restroom, where Kate learned that despite Wayne's abusive nature, Diane still loved him. Before she left, Diane warned Kate that if she ever sees her again, she will immediately call for help.
Kate fled to Miami under the alias "Monica", were she dated a police officer named Kevin Callis. Following the wedding, Kate called Mars and begged him to stop looking for her, which he agreed to do, under the condition that she would finally settle down, something that Kate knew she was incapable of doing. After almost becoming pregnant and Kevin's purchase of two Oceanic tickets to Costa Rica for their honeymoon, Kate confessed her fugitive past and laced his drink with a sedative before disappearing. After months of traveling around the country under numerous aliases, license plates and hairstyles, Kate learned that Diane was dying of cancer, and decided to visit her. She reunited with her childhood friend Tom, who helped her dig up their time capsule, containing a variety of items, including his small toy airplane. Tom, now a doctor, arranged a meeting between Kate and Diane. As Kate tried to apologize to her, Diane started screaming for help, prompting Kate to flee the hospital with Tom. A policeman opened fire on their getaway car, killing Tom and forcing Kate to flee the scene of the accident, leaving behind Tom and his childhood toy.
Months later Kate staged a robbery in New Mexico with several criminals to infiltrate a bank's safe deposit box, where the toy airplane was being stored, shooting the leader in the leg to prevent him from hurting the other customers and calling the police. She fled to Australia where, while sleeping in a barn, she was discovered by a farmer. Posing as a Canadian hiker, Kate worked on the farm for three months, saving her wages in a hole in the pantry. When the farmer caught her attempting to sneak away, and offered her a ride into town the next morning. During the journey however, Kate discovered that the farmer had learned of her true identity and notified Edward Mars of her whereabouts, in exchange for the $23,000 reward. Kate grabbed the wheel and crashed the truck into a field but instead of running, she helped the unconscious farmer from his vehicle, giving Mars time to pursue and arrest her. Escorting her to the airport in handcuffs, Mars briefed local security officers on Kate's fugitive past and revealed his locked carry-on case containing five firearms. Boarding the plane, he handcuffed Kate to her seat in the middle of the row, near the midsection of the plane. As the plane was bombarded with escalating turbulence, Mars was knocked unconscious by luggage from the overhead compartment. Kate stole the keys to the handcuffs and attached an oxygen mask to Mars before taking one for herself, as the plane splintered and crashed onto the island.
Having survived the crash, Kate discards her handcuffs and stumbles out of the jungle to encounter a wounded Jack, whose wounds she agrees to suture. That night, the two explore the inland area to search for the missing cockpit, accompanied by Charlie. The three discover the cockpit and Seth Norris, the surviving pilot. As they recover the radio transceiver, they are thrown into disarray by the arrival of the "Monster," whose rampage kills Seth. Kate returns to the beach with Jack and Charlie and later joins several survivors who accompany Sayid as he attempts to transmit a distress signal. Upon returning, Jack tells Kate that he knows she is a fugitive. She examines the injured marshal, only to be strangled. She asks Sawyer to kill him on her behalf, but he fails and only worsens Mars' condition, leading Jack to kill him. Later, after Jack discovers the caves, Kate decides to remain on the beach. She prepares to help Sayid locate the source of the looped distress call, but after Sawyer informs her of Jack being trapped in a cave in, she abandons her post to help. When Sawyer is being tortured by Sayid to find Shannon's missing asthma inhalers that they believe he has, he says he will tell her if she kisses him. After they kiss, he reveals he doesn't have them and Kate punches him.
When she discovers the marshal's case, she and Sawyer fight to gain possession, but she eventually informs Jack, who confiscates it from her. She later informs Nikki and Paulo of its original whereabouts. Kate helps Sun with her garden, learning that she understands English. Kate continues to maintain a helpful attitude throughout the camp, as she joins the search party for the kidnapped Claire and Charlie, returning only with the latter. When Claire returns two weeks later, Kate also helps capture Ethan. Later, Sawyer seeks Kate's help in tracking a boar he claims to be constantly harassing him. Kate jokes about his predicament, but agrees to help nonetheless. They camp out and reveal truths in a game of "I Never" where Kate admits she has killed someone. Whilst in the caves with Jack, she is sent to retrieve alcohol when Locke carries a mortally wounded Boone. She becomes sidetracked when she discovers Claire in the jungle going into labor, and must deliver the baby without Jack's help.
Kate grows concerned over Jack's well-being, and drugs him in order for him to get some deserved sleep. However, Kate and Jack later discover that the key to the gun case is missing; they find Shannon holding Locke at gunpoint later in the jungle. After Rousseau arrives on the beach to warn the camp of the Others' imminent arrival, she takes Kate, Jack, Locke, Hurley and Arzt to the Black Rock, where they attempt to carry dynamite to the hatch discovered in the jungle. After the sudden demise of Arzt, Kate volunteers to carry dynamite in her backpack; she discovers that Jack switched her bag moments before handing it to her. Arriving at the hatch, Kate helps prepare the dynamite. Once the hatch door is blown open, she and the others peer inside.
Despite Jack's objections, Kate and Locke descend into the hatch, Kate entering first. Once inside, she is caught by Desmond, and tells her to tie up Locke, until he reveals Kate's criminal past. Kate is tied up, gagged, and locked in the food pantry, where Locke slips her a knife with which to free herself. Kate crawls through the air vents and arrives in a room with a computer, where she overpowers Desmond after Jack arrives. She accidentally damages the computer in the crossfire, causing Desmond to panic and flee. When Jack returns, Kate is placed on a rotation to enter the numbers into the computer. As she and Jack play golf one day, they encounter Mr. Eko carrying a critically injured Sawyer. The rest of the tail-section survivors also arrive, along with Jin and Michael. Kate stays with Sawyer around the clock while he slips in and out of consciousness. Jack makes her take a break and asks her to go get some food for Sawyer. While picking fruit Kate sees a black horse from her past. When she returns to the hatch she hallucinates that Wayne is channeled through Sawyer and Kate freaks out. Later she is sitting in the jungle when Jack come along wondering what she is doing out here. She says she is sorry that she is not a perfect and good as him, and that this place (the island) is driving her nuts. Kate then kisses Jack passionately but then runs off while Jack calls for her. She partially confesses her crime to Sawyer who then wakes up. Kate leads Sawyer outside where they both see her black horse. When Michael runs off in search of his son, Kate volunteers to follow him, only for her offer to be rejected by Jack. Adamant to help, Kate follows them from a distance, but gets captured, tied up and gagged by Tom. She is held ransom for the weapons from the armory. Sawyer is angry and threatens Tom while Jack hesitates to give up the guns. However, just as Mr. Friendly is about to kill Kate, Jack gives up the guns and seems very angry with Kate. Sawyer sympathises with Kate, but Kate wants to talk to Jack the whole way back but Jack refuses to talk to her.
Later, Kate finds herself a victim of a long con, conducted by Sawyer, in order to gain access to the armory's remaining weapons and the camp's medicine. When Claire's baby falls ill, Kate joins her on a trek into the jungle to seek Rousseau's help. The three head inland, where they discover the Staff station. Inside, Kate examines the locker room, where she discovers a box of theatrical props and costume, including a fake beard worn by Tom. Failing to find what Claire was looking for, Kate returns her to the camp. Sun confides in Kate when she learns that she is pregnant, who helps her come to terms with the sudden news. Later, Kate and Jack discover a mysterious and unnoticed food drop in the jungle. They return to the hatch, where hostage "Henry Gale" is exposed as an impostor. Later, Kate joins Jack on a trek back to where they encountered the Others. On the way, they fall for one of Rousseau's traps, and are momentarily caught in a net together. The two make camp, where Kate apologizes for kissing Jack. He says he isn't sorry that she kissed him, then an exhausted Michael stumbles out of the bushes.
Michael invites her to follow him to the Others' camp when he recovers, to which she accepts. However, upon learning that Ana Lucia has stolen Sawyer's personal gun, Kate, Jack, Locke and Sawyer rush to the hatch to find her dead, and Michael and Libby severely injured. Kate scolds Jack when he decides to find the escaped Henry, reminding him that Libby is in dire need of medical assistance. Kate helps carry the two bodies to the beach, where she comforts Hurley over the loss of Libby. The next day, Kate, Jack, Sawyer and Hurley join Michael as they head for the Others' camp. On the way, Kate and Sawyer kill two of the Others who attempt to ambush them, causing Michael to reveal his true reasons for bringing them along. They are then ambushed, gagged, tied up and taken to a pier. Kate witnesses Michael leaving the island with Walt, while she, Jack and Sawyer are taken away with the Others.
Kate wakes up in a locker room, with Tom supervising her. She is forced to strip naked and shower and she then accompanies Ben for breakfast. Ben forces her to handcuff her hands and barefeet. She is then placed in a cage opposite Sawyer. The two are told to work for the Others, under the watchful eye of Pickett. When Sawyer rebels against the Others, one of the others, Juliet, holds Kate at gunpoint until he cooperates. Later, Kate climbs out of her cage and attempts to escape with Sawyer. Sawyer refuses to leave and finally reveals that there is no way off the island because they are on a different island than the one they crashed onto. The two have wonderful sex (unknown if it was oral or intercourse), unaware that they were being watched briefly by Jack on a surveillance video. Kate is then forced to watch as Pickett is about to kill Sawyer, in revenge for his dead wife. When Jack radios her via Pickett's radio, informing her that she has a head-start to escape, she and Sawyer lock Pickett inside the cage and run towards the beach. They encounter Alex, who gives them her boat in exchange for rescuing her brainwashed boyfriend, Karl. Upon arriving on the beach, however, Pickett holds them at gunpoint, until Juliet arrives and kills him. Jack radios her again, and tells her never to return for him. However, Kate is unable to abide by his request.
Upon arriving back on the main island, Kate demands that she and Sawyer head back to rescue Jack. When arriving on the beach, she scolds Sayid and Locke for not bothering to rescue him, telling them that she owes Jack. She heads into the jungle, with the two in pursuit, and finds Rousseau, who agrees to help her after learning of Alex's status. The four trek into the jungle, where they discover the Flame station. They are greeted by Mikhail, who poses as an innocent surviving DHARMA member, but is exposed as an Other. Kate and Sayid take him hostage, as well as Bea, found hiding in the basement. Upon leaving the station that night, Kate witnesses its destruction. The four, along with Mikhail, resume their hike, eventually coming across a set of sonar panel fences. Kate suggests climbing over them to avoid the sonic barrier, and the four eventually arrive at the Others' barracks, where Kate is appalled to see Jack bonding with Tom. Kate rushes in that night to rescue him, but is captured. Her hands and barefeet are tied and she is gagged as Jack explains what is going on. Later she is gassed and wakes up the next morning in the jungle, handcuffed to Juliet. The two constantly bicker as they are chased by the "Monster." They soon trap it outside the sonar fencing when Juliet unlocks the handcuffs. Kate finds Jack unconscious in one of the barracks, and apologizes for the trouble she caused. She returns to the beach with Jack, Sayid and Juliet.
Upon returning, Kate is still wary of Juliet. When Claire falls ill suddenly, Juliet explains to her and Jack about the deaths of pregnant women on the island. Kate grows concerned over the fate of Sun, and cautions her when she begins questioning Juliet. Later, she discovers Sayid with a satellite phone. She learns of Naomi's arrival, and of Juliet's true purpose for being in the camp. She breaks Sayid's word, and immediately informs Jack of Naomi's presence. That night, during a camp discussion, Jack and Juliet admit to being dishonest. Kate is then shown their plan to deal with the Others' kidnap attempt the next morning. However, after Karl arrives to warn then of the Others' imminent arrival, Kate travels to the radio tower with Jack and the majority of the camp. While going there Sawyer says she is going back to check on the others and Kate says she is going with him, but he says no. Juliet goes with him, but before she leaves she kisses Jack while Kate looks on. Later Kate is getting a rock out of her shoe when Jack comes over and tells her that Sawyer didn't mean it, that he was trying to protect her. He tells her that that is why he asked her not to go back for him. She askes him why he is sticking up for Sawyer and points out that Sawyer would never do the same for him. Jack replies: "Because I love you" while Kate looks on sadly. They eventually encounter Ben and Alex in the jungle, at which point Ben is taken hostage, while Alex is reunited with Rousseau. Kate arrives at the radio tower, where she witnesses Locke stabbing Naomi in the back. She watches as Jack makes contact with Naomi's freighter.
Moments after Jack and the group prepare to return to the beach, he and Kate notice that, whilst they weren't looking, Naomi's body has vanished. Kate goes to hug Jack as he sets off to find her, but instead steals the satellite phone from him and follows a trail of blood in a different direction from Jack. When the trail ends, Kate is ambushed by Naomi, who holds her responsible for attempting to kill her. Kate manages to convince Naomi that she and the rest of the group are innocent, and hands Naomi the phone when it starts ringing. When Naomi finally dies, Kate takes the phone and reunites with the group in the jungle by the cockpit. After a confrontation between Jack and Locke, Kate decides to stay with the former of the two, but questions Sawyer when he decides to go with Locke. Regardless, Jack and Kate remain behind while the two groups part ways, where they witness the arrival of Daniel. The three wander the jungle in search for the rest of his team, coming across a pack containing a gas mask. After finding Miles, Kate and Jack find themselves at gunpoint until she takes them to Naomi's body. After a while, they are rescued by Sayid and Juliet.
Later, the six of them meet up with Frank and the helicopter. Upon learning of the location of the final team member, Kate accompanies Sayid and Miles to the barracks. Upon arriving, the three of them find the barracks deserted, apart from Hurley who is locked in a closet. Moments later, Kate is kept quite by Sawyer while Locke and Rousseau seize the house. Kate decides to remain at the barracks, living with Claire, in an attempt to extract information from Miles. She arranges for him to speak to Ben, and sneaks him to where he is held. After being caught by Locke, Kate is told to leave in the morning, to which she spends the night with Sawyer and claims that she isn't pregnant. When Sawyer makes a remark about her torn between him and Jack, Kate slaps him before leaving. En route to the beach, she encounters Daniel and Charlotte, who knock her unconscious when she asks to look through their bag. Kate is found by Jack and Juliet, and follows them to the Tempest station to track down Charlotte and Daniel. Later, Kate tries to help Sun and Jin transfer to the barracks, only for her efforts to be interrupted by Juliet.
As she starts her first trial, she is forcibly put into handcuffs. During the trial, Jack takes the stand as a character witness, saying that Kate acted bravely and saved the lives of the Oceanic six demonstrating heroic self sacrifice. Kate appears to be unable to handle Jack's testimony and asks that he stop. On cross examination, the prosecution asks Jack whether he loves Kate. Jack becomes emotional and tells the jury that he no longer loves her. After Kate's mother refuses to testify, Kate takes a plea deal of probation, as she leaves the court house through a back exit she meets Jack who was tipped off by her lawyer. Jack tells Kate that he lied and that he still loves her. Kate asks him to stop by her house for a drink but Jack refuses and says he has to run for an errand. Kate understands that Jack does not want to see the baby. She leaves in a cab. When she gets home she is greeted by a woman who has been looking after her son. She goes upstairs to her son and hugs him while calling him "Aaron", Claire Littleton's son. Kate now looks after the baby off the island, due to the strange nature of the cover-up stories the Oceanic Six appear to be spinning.
In Something Nice Back Home, Kate is seen living in a relationship with Jack, who also acting as a surrogate father for Aaron, showing that Jack changed his mind about not wanting to see the child. Later, Jack asks Kate to marry him, which she happily accepts. After a series of strange events happening to Jack, he is seen starting to take pills and drinking. He later confronts Kate and after an argument Jack leaves. In the episode, Kate is also discovered doing undisclosed favors for Sawyer, who "chose to stay on the island". It is this fact that pushes Jack over the edge, ending their relationship - despite the fact that Kate tells Jack that this favor has nothing to do with them and their relationship.
In Through the Looking Glass, Jack and Kate's relationship is over, but after a series of calls from Jack, Kate agrees to meet him at an airport. Jack informs her of an unidentified person's funeral and she asks him why should she have gone. It is later revealed that the obituary is that of John Locke, under an alias of Jeremy Bentham. Jack then tells her that they need to return to the island. She leaves, saying that "He is going to be wondering where I am," referring to what we now know is Aaron. Jack shouts that they have to go back as she drives away.
Kate Austen is plagued by her inability to stay put. As a child, she has been described as straight A student. This lends credence to the idea that she wants to live a normal and happy life, but harsh circumstances have steered her away from her dream. She has spent a good part of her life running, which has ingrained in her an instinctual response to flee when things get hard or serious. We see this with her relationship with her former husband Kevin, and even her actions on the island in Season 1 and partially in Season 2 - she's manipulative with other survivors like Jack and Sawyer to get her way, much like a cornered animal. Her fugitive status has also caused her development to be severely arrested. In many ways, she is still very childish. For example, she is stubborn and does not listen to others around her, especially Jack. Moreover, she does not take accountability for her actions.
On the island, her character has become more and more defined by her romantic entanglements - namely, Jack and Sawyer. At different times, she has showed serious romantic interest in both men, making it hard to determine which she has stronger feelings for. Ultimately, she loves both men in different ways as they mean different things to her. Other than this, she is shown as strong, assertive, strong-willed, at times stubborn, and often as trying to prove her goodness to the other survivors by going on different, dangerous missions.
Off the island, it seems that her instinctual tendency to run has been put to rest, illustrating growth in her character. She commits to raising Aaron as her own son, and wants to marry Jack. The two actually enter into a very serious relationship, showing that she is ready to finally settle down. They appear to be thoroughly and genuinely happy for a time. However, aspects of her childishness have not changed, as she keeps secrets from her fiancee about a former lover, Sawyer, and expects him to just "trust her and let it be." Her inability to see the seriousness of keeping things from Jack only proves once again that although she has grown to be a loving mother, she is still unable to accept the consequences that come with her newfound responsibility.
Her influence does extend beyond sex appeal: Spiritual website Beliefnet named her among the Top 10 Most Empowering Women on TV Today, along with fictional characters Betty Suarez (from Ugly Betty) and Claire Bennet (from Heroes).