Was the second major writer for Marvel Comics after Stan Lee. Wrote various Marvel titles such as the Avengers in which he created the Vision. Also was the original writer for the Conan comic book revival and he also created The Invaders as well as other stories for the Company.
For DC Comics, has created titles such as the All Star Squadron & Infinity Inc. as well as scripts for various series, mini-series and one shots.
(2000-19) Ghostwriter for Stan Lee for the "Spider-Man" newspaper comic strip.