The Answer
Kessler
In the very first episode of Seinfeld called “The Seinfeld Chronicles”, Jerry’s neighbour wasn’t named Kramer. In fact, it was Kessler. In the first second if the clip below, you can hear Jerry refer to him as Kessler after he gives away the results of the evening’s Mets game that Jerry taped.
Near the end of the clip is a scene from Episode 2 where Jerry learns that the name really is Kramer. Kessler was a misspelling of his name from his apartment buzzer. (you can ignore the part in the middle which is seemingly unrelated).
The character is modelled after Larry David’s real-life neighbour, Kenny Kramer, but at the time of recording the pilot episode, they didn’t have the necessary rights and were somewhat reluctant to use the name.
Larry was hesitant to use Kenny Kramer’s real name for the fictional Kessler, because he suspected that Kenny Kramer would take advantage of this. His 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 character did indeed end up getting named Kramer, and the rest is history.
Happy Birthday to Michael Richards who turned 70 yesterday.