Kramer is the neighbor of main character Jerry Seinfeld, residing in Apartment 5B, and is friends with George Costanza and Elaine Benes. 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 taste in fruit; his love of occasional smoking, Cuban cigars in particular; his violent bursts through Jerry's apartment door; frequent pratfalls and his penchant for nonsensical, percussive outbursts of noise to indicate skepticism, agreement, annoyance, and a variety of other inexplicable responses. He has been described as "an extraordinary cross between Eraserhead and Herman Munster".

Kramer appeared in all but two episodes: "The Chinese Restaurant" and "The Pen", in the second and third seasons, respectively.

In "The Trip," Kramer hints that a man in a park attempted to expose himself to Kramer when he was a young boy. The extent of the offense is not revealed.

In "The Letter", Kramer tells two art patrons that he ran away from home at age 17 and stowed away aboard a steamer bound for Sweden.

Kramer never completed high school; however, it is learned in "The Barber" that Kramer has a GED.

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 in 1979 he was struck on the head by a falling air conditioner while walking on the sidewalk. Jerry asks if that was when Kramer lived in Greenwich Village, to which Kramer replies that he cannot remember. This is discussed in the beginning of "The Little Kicks".

In "The Strong Box", it was revealed that Kramer spent a brief time in the Army, although information about this time is "classified".

[Kramer's personality] is hard to pin down. A New York Times profile described Kramer as "cartoonlike" in a piece with a headline calling him "Seinfeld 's craziest neighbor". The Los Angeles Times calls him "eccentric" and "flipped-lid." To the Washington Post, he was "goofy". But he's more than so much concentrated comic schtick. Kramer is an attitude. Kramer 's revolutionary far more than he's "funny". He's liberating, a one-man guide out of stereotyped sitcom behavior toward the nut-ball stuff that really happens.