In the first episode of Seinfeld, Kramer's last name was Kessler. Producers were concerned that Larry David's friend Kenny Kramer (who was the bases for the character) would object to the use of his name. Eventually they worked out a deal and the character was renamed "Kramer"

Seinfeld was originally conceived as a one-off, 90 minute special called "Stand Up"

Jerry Seinfeld's former friend Michael Constanza sued the "Seinfeld" creators, claiming that the character of George was based on him and thus violated his privacy. He lost

Larry David provided the voice of the George Steinbrenner character in "Seinfeld"

Kenny Kramer, who was the basis for his namesake in Seinfeld, ran a bus tour through New York City which visited sites seen in the show. The bus tour was parodied in an episode of the show

Elain's New Yorker cartoon in a 1998 episode of Seinfeld actually made it into the real-life New Yorker