Kramer is the neighbor of main character Jerry Seinfeld, residing in Apartment 5B, and is friends with him, George and Elaine. Of the series' four central characters, only Kramer has no visible means of support; what few jobs he holds seem to be nothing more than larks.
His trademarks include his humorous upright hairstyle and vintage wardrobe, the combination of which led to his categorization as a 'hipster doofus'; his violent bursts through Jerry's apartment door; and his penchant for nonsensical, percussive bursts of noise to indicate skepticism, agreement, annoyance, and a variety of other inexplicable responses as well as his love of smoking and Cuban cigars in particular.
Kramer appeared in all but two episodes: "The Chinese Restaurant" and "The Pen", in the second and third seasons, respectively.
David was hesitant to use Kenny Kramer's real name because he suspected that Kramer would take advantage of this. David's suspicion turned out to be correct; Kenny Kramer created the "Kramer Reality Tour", a New York City bus tour that points out actual locations of events or places featured in Seinfeld. The "Kramer Reality Tour" is itself spoofed on Seinfeld in "The Muffin Tops." In the episode, when Kramer's life stories are used by Elaine for the use of various stories in Peterman's biography, he develops a reality bus tour called "The Peterman Reality Tour" and touts himself as "The Real J. Peterman".
In "The Betrayal", it is explained (as a retcon) that Kramer's original name given in the pilot, "Kessler", is just a misspelling on his mailbox.
Kramer never completed high school; however, it is learned in "The Barber" that Kramer has a GED.
It is jokingly implied in The Trip, Part 2 that Kramer was sexually abused as a child. A police interviewer trying to get him to confess a murder asked him if there was a pervert in the park with a present in his pants. After the interview, as Kramer is leaving, he asks the interviewer how he knew about the guy in the park.
Kramer was estranged for a long period from his mother, Babs. Unlike George Costanza and Jerry Seinfeld, Kramer's character does not have a well-developed network of family members shown in the sitcom.
During an opening discussion, Kramer revealed to Jerry that he was once struck on the head by a falling air conditioner while walking on the sidewalk. Jerry asks if that was when Kramer lived in the village, to which Kramer replies that he cannot remember.
Kramer has stated that his heroes are Mickey Mantle (who is also one of George's heroes), and Bette Midler.
In The Strong Box, it was revealed that Kramer spent a brief time in the Army, although information about this time is "classified".
In The Big Salad, Kramer mentions how he was brought up to be very punctual, and if he wasn't in bed by 9 o' clock, there would be serious consequences.
Kramer is known for his extreme honesty and, correspondingly, his lack of tact; in "The Nose Job", he tells George's insecure girlfriend that she is as pretty as any girl in New York City, she just needs a nose job. Instead of being horrified, many characters end up thanking Kramer for his candor. Kramer never gets into trouble for it, but his friends often do; this is especially prevalent in "The Cartoon" where Kramer makes comments to Sally Weaver (Kathy Griffin), who then blames Jerry for "ruining her life" as a result. He also gets his friends directly into trouble by talking them into things such as parking illegally in a handicapped space ("The Handicap Spot") or urinating in a parking garage ("The Parking Garage").
Kramer is known for taking items from Jerry, most notably food. Jerry's apartment is Kramer's second home (at one point he calls Jerry's phone "line one" and his own "line two"); he has his own key to the apartment, almost never bothers to knock, and even begins to receive phone calls there in "The Pilot". It is revealed in "The Betrayal" that this may be due to Jerry's offer upon moving into the building (12 years earlier, about 4 years before the first episode), telling Kramer, "We're neighbors. What's mine is yours."
One explanation as to Kramer's personality and traits, with respect to his mysterious childhood and background, is hinted in "The Chicken Roaster". After a series of conflicts, Jerry is forced to live in Kramer's apartment and vice-versa, which quickly has an effect on both characters. Jerry, bothered endlessly by the many problems in Kramer's home, quickly begins acting like his wacky friend, showing that Kramer might be radically influenced by his own apartment but has simply grown used to it. Of course, when Kramer finally begins living in Jerry's regular and normal apartment, he quickly and briefly becomes more like his calm and quick-witted friend.
His relationship with George and Elaine is as moderately strong as with Jerry. He helps Elaine in "The Watch", "The Engagement", "The Soup Nazi" and "The Slicer", and helps George in "The Busboy", "The Stall" and "The Slicer". His conflict with Elaine is "The Seven" and with George in "The Susie".
His relationship with Jerry is very questionable. Simply put, Jerry is usually reluctantly persuaded into doing things. Kramer also at times gets into arguments with Jerry, in episodes such as "The Chaperone", "The Kiss Hello" and "The Caddy". On the other hand, Kramer has displayed an almost unbending loyalty toward Jerry in many episodes, especially when choosing to help him against Newman in many episodes, including "The Suicide" and "The Millennium". In the same respect, Jerry has helped Kramer out of good will in some episodes and always seems to forgive and ultimately accept his friend's mooching tendencies. Their friendship, at least on Kramer's side, is so close in some manner that Kramer sometimes has an acting shot of Jerry framed on his wall during the fifth season, notably in "The Marine Biologist".
His relationship with Newman is defined from the start in "The Suicide", in which he gets along very well. Like the main characters, they also get into conflict with each other. Their "quick rich schemes" are noted in "The Old Man" and "The Bottle Deposit". The most notable conflict other than each other is Keith Hernandez in "The Boyfriend" until the baseball star straighten out the facts along with the famous JFK parody.
His relationship with Susan is mixed. Although he gets along in "The Secret Code", there are many episodes in which he made her life in a mess. He vomited on her in "The Pitch", unwittingly burned her father's cabin in "The Bubble Boy", dated Mona while Susan was a lesbian in "The Smelly Car" and calls her "Lily" in "The Invitations". Due to his indifference to what's going on, his reaction to Susan's death is "to get some coffee".
Much of Kramer's lifestyle is "out-of-date", including his clothing, which is often a size too small or large and years (or decades) out of fashion. He seems to shop at second-hand stores and has no concept of style or taste. Kramer thinks of himself as a very "with-it" individual, up-to-date on everything, but is constantly being shown to be ignorant, uninformed, and foolish. He often drives large, old American sedans, such as a 1973 Chevrolet Bel Air, or a 1985 Ford LTD. To all this, Kramer is oblivious and he makes no note of other people's opinions of his lifestyle and views.
Kramer's trademark spruced-up hairstyle is unique. Elaine has pejoratively described it as "like the bride of Frankenstein." The only episodes in which his hair changed were "The Apartment" and "The Good Samaritan," in which he used mousse in his hair, and "The Shower Head," in which a low flow shower head was installed in his shower, preventing him from getting all the shampoo out of his hair.
Kramer's own apartment is sub-let from documentary filmmaker Paul Buchman from Mad About You. Kramer's apartment is the subject of numerous radical experiments in interior design, including "levels" (no furniture) in "The Pony Remark", and a reconstruction of the set of The Merv Griffin Show in "The Merv Griffin Show". Inside views of Kramer's apartment are seldom, but it is known that he installed hardwood flooring and woodgrain-like wallpaper to, as he explains to Jerry, "give it the feel of a log cabin." The apartment is centred around a large hot tub and couch styled after a 1950s Cadillac.
Kramer's signature on the show is entering a room by sliding in, much like Art Carney's character in The Honeymooners. This reportedly first became a recurring gag when Richards was late for a cue; trying to save the scene, he burst into the room, much to the delight of the audience. His initial bursts into Jerry's apartment were fairly conventional, and became somewhat more flamboyant or physically comedic as the series progressed. He is also known to be very clumsy, constantly tripping over things and knocking things down. By the end of the series, The Notes About Nothing counted Kramer entering Jerry's apartment 389 times, although the true amount is debatable based on entrances only heard and times when Kramer is already in the apartment.
In "The Visa", George commented, "Kramer goes to a fantasy camp. His whole life is a fantasy camp. People should plunk down two thousand dollars to live like him for a week. Do nothing, fall ass-backwards into money, mooch food off your neighbors, and have sex without dating. That's a fantasy camp."
Kramer has also been show to be very interested in Canadian culture; in one episode Jerry mentions that Kramer wouldn't be interested in Super Bowl tickets because he only follows the Canadian Football League. In another episode, Kramer mentions to Jerry that he is taping the Canadian parliament on C-SPAN.
In the episode "The Raincoats," he panics when the word "mouse" is mentioned.
He has seizures whenever he hears the voice of Mary Hart, co-anchor of the show Entertainment Tonight, as seen in the episode "The Good Samaritan" (incidentally, at least one real-world case of so-called 'Mary Hart epilepsy' has been reported in North America). 
In the episode "The Betrayal," Kramer's friend FDR (Franklin Delano Romanowski, played by Michael McShane) wishes on his birthday candles that Kramer would drop dead, after Kramer threw a snowball at him. Kramer tried to get 100% anti-drop dead protection for life, but lost after losing a wishbone break. FDR dropped his "drop dead" wish towards Kramer after they both agreed that FDR could launch a snowball at Kramer's head.
Kramer is inexplicably popular with both George's and Jerry's parents, although this isn't true at first. In "The Handicap Spot," Estelle calls Kramer "trouble" and expresses her dissatisfaction at her son hanging around him. It is revealed in "The Blood" that he calls the Seinfelds once a week (as he explains to Jerry, "If you called them more often, I wouldn't have to."). George's parents let Kramer stay at their house in an episode when they are away on a trip. They even let Kramer have a "girl over" (which George explains they never let him do). He even briefly moves into Jerry's parents' retirement community in Florida, where Morty Seinfeld recruits him to run for Condo Board President in an attempt to establish a puppet régime. Kramer even manages to befriend the "Soup Nazi," which seemed impossible because of the Soup Nazi's short temper and his outbursts at anyone who holds up the line.
The only steady job Kramer is known to have had was in "The Strike", when he went back to work at H&H Bagels after being on strike for over a decade. His union finally settled the strike when the minimum wage of New York was raised to the hourly rate Kramer had been demanding from his employer (Kramer still felt the strike was a success), and he was re-employed. He only worked there during that one episode before he was fired. During the time he was working at the bagel shop, he went on strike again because of having to work during Festivus, a holiday invented by Frank Costanza.
Kramer has engaged in a variety of short-lived jobs. He worked part-time as a department store Santa before being fired for spreading Communist propaganda to young children in "The Race". In "The Bizarro Jerry", he worked at an office where he was not actually employed, describing his daily activities to Jerry as "T.C.B. You know, takin' care of business." His "boss" eventually "fires" him, commenting that his reports resemble work by someone with "no business training at all." In "The Beard", he was paid to be a decoy in a police lineup. A story arc of the fifth season included Kramer's idea for a coffee table book about coffee tables, which was eventually published in "The Fire". His success in that particular endeavor was short-lived, however, because he spilled coffee on Kathie Lee Gifford while promoting the book on Live with Regis and Kathie Lee in "The Opposite". In The Pick, he became an underwear model for Calvin Klein, which must account for at least some of his income. The biggest boost to Kramer's income would have to be in the episode "The Wizard" when his coffee table book is optioned for a movie by a "big Hollywood so-and-so", earning Kramer enough royalty money to retire to Florida (although he moved back to New York almost immediately after a "political scandal" involving going barefoot in the clubhouse, which cost him the election for condo board president.)
He is a compulsive gambler who successfully avoided gambling for several years until "The Diplomat's Club", in which he bet with a wealthy Texan on the arrival and departure times of flights going into New York's LaGuardia Airport. Earlier than that, "The Pony Remark" and "The Subway" still shows that Kramer is a tough gambler.
A struggling actor, Kramer briefly lived in Los Angeles, where he accosted Fred Savage, appeared in a cameo on Murphy Brown, and was a suspect in a string of serial killings ("The Keys", "The Trip"). Back in New York, Kramer worked as a stand-in on a soap opera with his friend Mickey Abbott in "The Stand In", and was given a one-line part in a Woody Allen movie in "The Alternate Side" (His line, "These pretzels are making me thirsty", became the show's first catch phrase.), but he was fired before completing his scene. Kramer has worked in various other theater projects, such as acting out illnesses at a medical school in "The Burning".
In the episode "The Strong Box", Kramer says one of the things in the box is his military discharge. Upon being asked, "You were in the military?", Kramer replies, "Briefly."
Kramer's financial status seems to be contradicted across episodes. For example, in one episode George asks Kramer if he can break a twenty-dollar bill, to which he replies, "I only have hundreds" ("The Mango"). However, in another episode, in which he explains to Jerry that wallets are a nuisance and that he should use a money clip, Kramer advises Jerry to "keep the big bills on the outside" and shows Jerry his own money clip as an example, to which Jerry responds, "That's a five" ("The Reverse Peephole"). When Kramer decides to pay off Jerry (for all the food that he took from Jerry in a week) which was $50 he says "I dont have that kind of money" and he ends up selling his bicycle to Newman to settle Jerry.
Kramer showed an entrepreneurial bent with "Kramerica Industries," for which he devised plans for a pizza place where customers made their own pie ("Male Unbonding"), a bladder system for tankers that would "put an end to maritime oil spills" ("The Voice"), and a product that would put ketchup and mustard in the same bottle.
He also came up with the idea of a beach-scented cologne in "The Pez Dispenser", but a marketing executive for Calvin Klein informed him that the idea was senseless. However, in "The Pick", it is revealed that Klein has produced a cologne called Ocean based on the same idea. When Kramer confronts him about this, his interaction with a Klein executive lands him a photo shoot in connection with the cologne as an underwear model.
In "The Doorman", Kramer and Frank Costanza co-develop a prototype for a brassiere for men called the "bro" or the "mansiere". It's mentioned again in "The Fusilli Jerry" when Frank believes that Kramer used "the move".
In "The Muffin Tops", Kramer cries foul after failing to receive due credit for J. Peterman's book success which was unduly based on Kramer's misadventures. He then confronts Peterman during a book signing, and is kicked out of the event. Kramer then declares himself to be "The Real Peterman" and initiates The Real Peterman Reality Bus Tour, charging customers $37.50 for a tour of his life. On the matter of this tour, Jerry commented that it was "basically $37.50 for a mini 3 Musketeers bar."
Kramer also hatched a scheme to smuggle actual Cubans to the United States to make his beloved outlawed Cuban cigars, only to learn the "Cubans" are actually Dominicans ("The English Patient").
He participates in lawsuits against various people and companies, represented by Jackie Chiles, a parody of Johnnie Cochran. In "The Maestro," he settled one such suit (though he received no monetary compensation) against a coffee company whose beverages were too hot (a reference to the McDonald's coffee case). In "The Abstinence," Kramer sues a tobacco company for the damage its products caused to his appearance, and in "The Caddy," he sued Sue Ellen Mischke for causing a traffic accident that ruined his chances at becoming a professional golfer.
In "The Opposite", Kramer goes on Regis and Kathie Lee to promote the book. By accidentally spitting his coffee over Kathie Lee Gifford ("All over my Kathie Lee Casuals!"), his book tour immediately goes down in flames. Also in the episode, as a result of a bizarre chain of events, Elaine inadvertently causes the end of Pendant Publishing and therefore the end of Kramer's book. Nevertheless, the book is mentioned later in the episode "The Wizard" where it is revealed that the book was being made into a movie and the money Kramer makes causes him to move to Florida temporarily.
The book itself was full of pictures of celebrities' coffee tables, and even had a pair of foldable wooden legs. He also said that he had plans for a coaster to be built into the cover, and it is unknown if this feature was actually implemented at any point.
Under the name H.E. Pennypacker in "The Puerto Rican Day", Kramer poses as a buyer interested in an apartment in order to use its bathroom. Kramer appeared as A.G. Pennypacker to help Elaine get revenge on a store, Putumayo, by repricing all the merchandise in the store with a pricing gun ("The Millennium"). In the latter capacity, he claimed to be "a wealthy American industrialist."
As Dr. Martin von Nostrand, Kramer tried to get Elaine's medical chart to erase the negative comments her doctor had made in "The Package". He also used the von Nostrand alias in the episode "The Slicer", posing as a dermatologist for a cancer screening at Kruger. Kruger later recognised him as Dr. von Nostrand in "The Strike". Kramer used the name Martin von Nostrand (without the "doctor" prefix) while auditioning for the role of himself on the show Jerry in "The Pilot, Part 1". Kramer posed as Professor Peter von Nostrand in "The Nose Job" in order to retrieve his jacket from another man's apartment.
Kramer was also referred to as "Assman" in reference to the license plate the state of New York accidentally gave him in "The Fusilli Jerry". Occasionally, he is called "the K-Man" ("The Barber", "The Bizarro Jerry", "The Busboy", "The Hamptons" and "The Soup Nazi").
A derogatory designation for Kramer has been "hipster doofus", a moniker assigned to him by a woman in a wheelchair he once dated in the episode "The Handicap Spot", and occasionally directed at him by Elaine, as in "The Glasses". The nickname was first used in a newspaper review of Seinfeld.