Lucas Roberts came to Salem with his mother Kate Roberts, upon returning from military school in 1993. Upon arrival, he befriended Sami Brady and the two began their scheming relationship that continues to this day. Sami wanted Austin Reed, who was in love with her sister Carrie Brady, and Lucas wanted Carrie, who was in love with Austin. Lucas told Sami that if she lost some weight she might get Austin to notice her, so Sami went on a crash diet. Meanwhile, Lucas managed to convince Carrie to have plastic surgery on her scar so she could be Bella's Face of the 90s. Later, Lucas learned that his illegitimate father was Bill Horton and that Austin and Billie Reed were his maternal half-siblings.
When Lucas' friend from school Alan came to town, he raped Sami and took Carrie and Sami hostage. After Alan went to jail, Sami feared that nobody would ever love her. Lucas was feeling rejected by Carrie. Both seeking comfort, Lucas & Sami slept together. Soon after, Sami drugged Austin and tricked him into sleeping with her too by pretending to be Carrie. Carrie learned that Austin had slept with someone else, but she didn't know it was her own sister. Austin & Carrie were apart because they both suspected the other of being unfaithful.
After Lucas' mother Kate was apparently killed in a plane crash, he learned that Vivian had something to do with it and he blackmailed her into finding Sami and bringing her home in time to stop Austin and Carrie's wedding. Sami returned and revealed that she was pregnant with Austin's child. What Lucas didn't yet realize is that he was baby Will's true father.
Sami's plots continued and eventually brought Carrie & Lucas together, freeing up Austin for Sami. Eventually, Lucas's mom Kate learned the truth and exposed both Lucas and Sami. Carrie and Austin were reunited. However, a later accident left Sami with amnesia, which Lucas used to his advantage. He pushed Sami towards Austin, to keep him away from Carrie. Even as Sami's memories started to return, Lucas convinced Sami to help him with a new plot to convince Austin that Carrie was falling in love with Mike Horton. Lucas thought that once Austin gave up on Carrie, he could easily steal her from Mike. Once Austin was free, Sami was planning to steal him from Carrie.
As usual, the truth eventually came out, and Austin & Carrie married. Lucas learned that Sami was blackmailing his mother, but Kate refused to tell him what Sami had on her. After Sami became engaged to Franco Kelly, Lucas refused to let Franco become Will's stepfather. Franco was later murdered and Sami was charged with the crime, although Lucas was the culprit. Sami was almost executed, but Lucas confessed at the last possible moment.
Lucas later fell in love with Nicole Walker, but she was in love with Eric Brady, Sami's twin brother. Lucas didn't realize that his mother had paid Nicole five million dollars in 1999 to marry Lucas so that he would win custody of Will. The plan worked, but after Sami was released from prison, she worked with Nicole to get Will back. Nicole got Lucas drunk and seduced him and made him think he had beaten her and he confessed to Franco's murder. They were divorced less than a year after being married.
After being injured in a fire-blaze his mother purposely lit in the Kiriakis Mansion, Lucas was sent away to a rehab center in 2001 due to his alcohol addiction.
Lucas came out of his coma a year later and came back to Salem, but he was still partially paralyzed. Lucas seemed to really want to make amends, but showed his true colors at Austin and Sami's wedding when he exposed the truth and ruined the wedding. Eventually, with Victor's help, Lucas got joint custody of Will, whom he took with him for a summer in Africa.
Upon their return, Lucas went from being strongly on Victor's side to working for his nemesis, Tony DiMera. He enjoyed his new power, but the stress drove him back to drinking. His AA sponsor, Maggie Horton, told Lucas he would feel compelled to drink until he was truthful about his feelings. Lucas managed to control the drinking, especially after Sami was injured at the DiMera Mansion and nearly died. While she was in the hospital recovering, Lucas kept fantasizing about her. He continued to help Sami adjust after she got out of the hospital.
Lucas, as well as his mother, was one of the main suspects when the Salem Stalker started a murder spree. When the Stalker's identity was revealed to be Sami's mother, Marlena Evans, Lucas comforted Sami. She and Lucas grew closer as he tried to help her through this difficult time, and they finally made love again. Lucas even proposed to Sami, but with a caveat: she had to promise to redeem herself and never lie to him again.
Sami and Lucas became engaged but Kate did everything in her power to make sure they never walked down the aisle. She even brought Sami's ex, Brandon Walker, back to town. With Kate's help, "fate" intervened. Lucas found Sami and Brandon in bed together on the morning of the wedding, and he was devastated. As much as he loved Sami, he couldn't forgive her for this. He ripped up the marriage license and swore he never wanted anything else to do with her. Sami tried to convince him that Kate was responsible, but his mother smooth-talked him and he only further blamed his ex-fiancé.
Lucas joined the team to rescue his half-brother Philip Kiriakis, unaware that Sami (disguised as Stan) had infiltrated the group with a plan of her own. Back in Salem, with Philip's rescue successful, Lucas and Sami grew close again and became engaged. On their wedding day, Lucas's mother arrived at the chapel dressed in Sami's Stan costume. She exposed Sami's escapades, and Lucas dumped Sami at the altar. Austin, arriving for his half-brother's wedding, showed up just in time to comfort Sami.
In 2006, Lucas accepted a job with his former stepfather, Victor Kiriakis, and traveled to California to investigate a possible takeover of High Style. To his surprise, his old flame Carrie Brady had left Mike Horton in India and was the head of the company. He convinced her to return to Salem. At first, Carrie and Austin seemed to reconnect. But Carrie admittedly had feelings for Lucas, too.
Carrie agreed to marry Lucas, although she loved Austin, because she thought (through a plot of Sami's) that she could not have healthy children with Austin. She also believed that she was pregnant with Lucas's child. She and Lucas moved into an apartment across from Austin and Sami, who had seemingly reconciled. Shortly after Carrie's wedding to Lucas, she realized that she was never pregnant at all. That, along with the sexual tension between the two mismatched couples, resulted in a quick annulment for Carrie and Lucas.
Meanwhile, Austin and Sami became engaged, but on her wedding day Sami called off her wedding to Austin because a mysterious gloved hand was blackmailing her.
Sami began a short relationship with her neighbor EJ Wells, who was later discovered to be Elvis DiMera. Lucas became jealous of the relationship and with the help of their son Will, Lucas and Sami were reunited. While away on a ski trip, snow caused the roof of the cabin to fall on Lucas, causing him to be knocked unconscious. Sami left to find help and flagged down a car driving by. In the car was EJ, presumably fleeing after shooting John Black. EJ told Sami that he would help her save Lucas if she let him have sex with her. She was disgusted, immediately referred to his proposal as rape, but unwillingly submitted in order to save Lucas' life.
Sami became pregnant, and she and Lucas became closer than ever. Lucas proposed, and they became engaged again. Unlike the many other times, they got married successfully. On their wedding night, Sami confessed everything to Lucas about EJ and the questionable paternity of the baby. Lucas was distraught, wanting to kill EJ for raping her. He expressed shame over the man he had been - not standing by Sami in the past - and tearfully apologized, stating it was his fault Sami felt she couldn't come to him after being raped and tormented by EJ. He vowed to be a better man for her, the kind she can depend on.
After taking an amnio test, Lucas was found out Sami wasn't having one baby, but two babies. A fake report was created by Nick Fallon, blackmailed by Kate Roberts, that EJ was indeed the father of both babies. However, upon actually having the test run, Nick found out that Lucas is the true father of both twins. On October 23, 2007, Sami gave birth to the twins, a boy and a girl. After it was noticed that the twins did not look alike even for fraternal twins, a second DNA test was done. This time the test revealed that Lucas was not the father of Johnny, that was EJ Wells, but he was the father of the little girl.
With he and Sami divorced and Sami now married to EJ, Lucas is attempting to change his name to Horton. On December 20, Lucas revealed to Kate that he hired a nurse to watch Johnny and Allie and went to the church and got his gun and shot EJ. He has confessed and is going to prison for shooting EJ in the back.
On May 19, 2008 Mickey Horton informs Lucas of the possibility of being released and put under house arrest.
At Statesville Prison, Lucas was excited to be going home. Mickey reiterated that he would still be completing his prison sentence, only he’d be doing it under house arrest at home with his family. Lucas was eager to get out as soon as possible. Mickey implored him to read the terms of his release first, warning him that they have to be followed to a “T.” Otherwise, his house arrest will be revoked and he’d have to serve out the remainder of his sentence in prison. Mickey also stated that he’d be given an ankle monitor that he’d have to wear at all times. Mickey confessed that Sami took the twins and moved to the DiMera mansion with John and Marlena. Upon arriving at the DiMera mansion, Lucas walked in on EJ and Sami in bed. Lucas couldn't believe Sami had betrayed him. Sami apologized to Lucas and vowed to be true to him. Lucas soon discovered a way to remove his ankle monitor without the alarms sounding. Soon after being place under house arrest, Lucas developed a friendship with Chloe Lane, and went to meet her at the Salem Inn. While in the elevator there, the power went out, and Lucas and Chloe ended up making love. He was soon discovered and sent back to Statesville prison.