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 energetic 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.
The character of Kramer was originally based on the real-life Kenny Kramer, a neighbor of co-creator Larry David from New York. However, Michael Richards did not in any way base his performance on the real Kramer, to the point of refusing to meet him. This was later parodied in "The Pilot" when the actor that is cast to play him in Jerry and George's sitcom refuses to base the character on the real Cosmo Kramer. At the time of the shooting of the original Seinfeld pilot titled "The Seinfeld Chronicles", Kenny Kramer had not yet given consent to use his name, and so Kramer's character was originally referred to as "Kessler".
Larry 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."
Cosmo Kramer was known only as "Kramer" during the show's first five seasons (from 1989 to 1994), though in the pilot, "The Seinfeld Chronicles," Jerry referred to him as Kessler, which was his original name for the show, until they changed it to Kramer. George finds out his unusual first name through an encounter with Kramer's long estranged mother, Babs (played by Sheree North), in the season six episode, "The Switch". Despite this, most characters continued to call him Kramer for the remainder of the show's run (although many minor characters did refer to him as "Cosmo").