Before Mark Millar started churning out works of unfettered shock value more akin to movie pitches than actual, full-fledged comic book stories – e.g. Kick-Ass 2, Nemesis, Superior, et cetera – he made The Ultimates, otherwise known as The Avengers of the Ultimate universe.
The characters therein resembled the ones we knew from the 616 universe, only they were a bit darker and more complicated – more "modern," if you will. Iron Man was a wealthy, drunken bachelor terminally ill with cancer; Thor was an environmentally-minded hippie – an actual god (?) or a just crazy guy with super-advanced technology (?); Hulk was a man-eating monster that could barely be contained, let alone harnessed for good; and Captain America was an old-fashioned John Wayne-type with ultra-patriotic sensibilities.
All-in-all, it was pretty awesome, not to mention gorgeous, thanks to Bryan Hitch's picturesque, semi-realistic artwork. Much of the Ultimate Universe – and The Ultimates in particular – has greatly influenced Marvel’s filmography, from Sam Jackson's portrayal of Nick Fury to Captain America's more streamlined and militaristic costume to Hawkeye’s role as a S.H.I.E.L.D. agent. Which is why The Ultimates is the closest thing to required reading for Joss Whedon’s The Avengers that exists in Marvel’s massive catalog.