More than fifteen years before the modern era in the Ultimate Universe, Marvin Flumm a.k.a. Mentallo was being exploited as a source for Mutant Growth Hormone. Toad was cultivating the drug from Flumm's vegetative body and tried selling the franchise to Wilson Fisk before being taken down by S.H.I.E.L.D.
In the present, Agent Marvin Flumm of S.H.I.E.L.D. was an ambitious black ops agent who hated the Ultimates and wanted Nick Fury's job. With the backing of a shadow cartel in the American government, Flumm moved to seize control of S.H.I.E.L.D. while Fury was off-site, orchestrating Winter Protocols. His attempt at using the Hulk to attack Reed Richards and his futuristic City was a debacle, leading Richards to assassinate the President and most of Congress with a suicide bomber. The exchange of power left Flumm in charge, despite his poor showing as director and obsession with hunting down rogue Ultimates agents. When Steve Rogers won a write-in vote for the new President of the United States, Flumm attempted to assassinate Rogers on behalf of his allies. He was caught by Captain America and Black Widow, charged with treason and removed from his position.