Zepp is an afterlight who died in the crash and hydrogen fire of the revered passenger air craft, the Hindenburg (a.k.a. Zeppelin LZ-129). He is never actually seen in the story, but hails from Germany and gave air rides to afterlights who bartered with him using any possessions they had. Some time before the events of Everlost he gave away the Hindenburg to Speedo in exchange for numerous quantities of bratwurst.
Zepp died in the Hindenburg crash and fire in May of 1973 along with 35 other passengers. Unlike the other deceased travelers, he crossed into Everlost along with the Hindenburg. Some time after his awakening, he took control of the air craft and began to give rides to any afterlights who could give something of value to him. Between his death and the events of the book, he gave the Hindenburg to Speedo in exchange for bratwurst.
Not much is known about Zepp's personality, but it can be assumed that he was eccentric and hospitable to an extent due to his air transportation system.
Zepp's appearance is never revealed in the book.
Zepp is mentioned by the narrator when Speedo unveils the Hindenburg to Nick, Vari, and Mary. His background and death are revealed and his system of transporting afterlights is also mentioned. The German boy's exchange with Speedo is revealed as well, explaining how the finder came across the Hindenburg.