Geldoff is a fictional character in Marvel Comics who 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 into Earth-616 by Dan Slott and Christos N. Gage in Avengers: The Initiative #8 (February 2008) where he was given the code name Proton.