 In the first episode Jerry calls Kramer "Kessler". The characters  name was subsequently changed to Kramer. In the episode "The  Betrayal", towards the very end when we see the scene from "Eleven  Years Earlier", Jerry is moving into his apartment, and Kramer comes  over to welcome him. Jerry says, "You must be Kessler, I saw your  name on the buzzer," to which Kramer replies, "No, its Kramer."