Geldoff is a fictional character appearing in American comic books published by Marvel Comics. He first appeared in the Ultimate Marvel Universe's Ultimate Spider-Man #40 (July 2003) written by Brian Michael Bendis with art from Mark Bagley. Geldoff was brought to Earth-616 by Dan Slott and Christos N. Gage in Avengers: The Initiative #8 (February 2008), where he was given the code name, Proton.