Mark Gruenwald was a writer and editor for Marvel Comics, the comic book company that produced official adaptations of the adventures of various super-heroes that lived in New York City during the Modern Age of Heroes. In his first recorded appearance he accompanied staffers George Perez and Ralph Macchio to an art showing in SoHo that featured the works of Alicia Masters. The event was crashed by long time Fantastic Four foes the Terrible Trio. The three Marvel staffers were witnesses as the Trio were defeated by the Thing and the Impossible Man. Not long after this, Gruenwald was at the Marvel Comics office discussing with staff how to properly render Ka-Zar's animal companion Zabu when the sabretooth tiger came crashing into the offices with the Impossible Man, part of the alien's planet wide scavenger hunt. Apparently unable to get away from the Impossible Man, Gruenwald was witness as the trouble-maker clashed with Warlock at Manhattan's Pier 7, another alien shape-shifter.
Sometime after this, Gruenwald apparently needed to take High School Diploma equivalency test in Virginia. Among those taking the test was Lemar Hoskins, who was secretly the super-hero known as Battlestar. Gruenwald frequently ended up working with fellow Marvel editor Tom DeFalco. The pair were first seen working together with the She-Hulk. The two Marvel staffers attempted to help She-Hulk find a new writer for her comic book series after the departure of regular writer/artist John Byrne. On a cruise with DeFalco, both her and Gruenwald was washed ashore of an island run by occultist Doctor Druid when their ship sank. Allowed to stay the night, DeFalco accidentally caused an explosion when he lit a cigar in a gas filled room. Later Gruenwald and DeFalco celebrated the holidays, and lacking any money of their own utilized the company credit cards to buy gifts for each other.