As a writer, Gruenwald is best known for creating the Official Handbook of the Marvel Universe and his ten-year stint as the writer of Captain America during which he contributed several notable characters such as Crossbones, Diamondback and U.S. In 1982, Gruenwald, Steven Grant, and Bill Mantlo co-wrote Marvel Super Hero Contest of Champions, the first limited seriespublished by Marvel Comics.

During this period, he shared an office with writer/editor Denny O'Neil, whom Gruenwald considered a mentor.

Hired initially as an assistant editor in January 1978, Gruenwald was promoted to full editorship by Marvel editor-in-chief Jim Shooter in 1982, putting Gruenwald in charge of The Avengers, Captain America, Iron Man, Thor, Spider Woman, and What If. In 1978 he was hired by Marvel Comics, where he remained for the rest of his career. Articles by Gruenwald include 'The Martian Chronicles' (a history of the Martian Manhunter) in issue #13 and several articles on the history of the Justice League in issue #14. Before being hired by Marvel, he wrote text articles for DC Comics official fanzine, The Amazing World of DC Comics. Collecting SQUADRON SUPREME (1985) #1-12 and CAPTAIN AMERICA (1968) #314.Gruenwald got his start in comics fandom, publishing his own fanzine, Omniverse, which explored the concept of continuity. Can their plan succeed? Will a renegade member bring about their downfall? And what will happen when this Earth's mightiest heroes find themselves becoming instead its all-powerful, totalitarian overlords? Before Watchmen, before MARVELS, before Kingdom Come - there was Squadron Supreme, a deconstructionist parable of the super-hero paradigm in a real-world setting considered by many to be the late Mark Gruenwald's finest work. Faced with the possibility of a new dark age for mankind, they choose the only course available to them - and take control of the world's governments themselves! Now, they have one year in which to completely restructure human society. On an Earth much like our own, the world's greatest superhuman champions are confronted by a society in ruins.

Squadron supreme by mark gruenwald