Today, Iron Man is one of the most well-known superheroes in the Marvel Universe - but in the 90s, the character was so unpopular that he missed out on the single biggest crossover event of the decade. The 1990s, sometimes known as the Dark Age of Comics, saw a series of stories that sought to shake-up the status quo (killing Superman, revealing Spider-Man as a clone, etc). But in 1996's Marvel vs. DC, written by Ron Marz and Peter David with art by Dan Jurgens and Claudio Castellini, nearly every Marvel hero took part in the battle to save the universe - except Tony Stark.
In Marvel vs. DC, the two biggest comic book universes merge without warning. The Joker escapes Spider-Man, Bane attempts to break Captain America's back, Wolverine steals the Batmobile, and a dozen other superhero encounters ensue across the Earth. The reason behind the merge is frightening: two "Brothers", each representing the Marvel and DC universes, wish to fight one another. Since a fight between these two powerful entities would result in the destruction of both universes, each Brother chooses champions to fight in their stead. The side that loses the most battles loses their universe forever.
Eleven fights are depicted throughout the series. The outcome of the first six was decided by the writers, and the remaining five were decided by fans voting through mail. That led to some interesting outcomes where popularity decided the match: Wolverine somehow defeated Lobo despite the latter's powers, and Spider-Man managed to electrocute Superboy into unconsciousness. But Iron Man - one of the original founding members of the Avenges - did not fight a single DC hero. In four issues, he doesn't even get a line.
The above image is the only appearance of present-day Iron Man in the entirety of Marvel vs. DC (outside of a flashback image of the core Avengers - but Tony is in the background and the panel is actually about Captain America). Popularity decided who fought and who did not, which is why characters like Jubilee and Superboy are involved and the Fantastic Four are on the sidelines. The decade was dominated by Spider-Man and the X-Men (which is why no less than three mutants found spots on the roster), and Iron Man was seen as a behind-the-times hero who didn't represent the younger generation.
Considering the runaway success of the Marvel Cinematic Universe and Iron Man taking center stage in most of the films, it's odd to see the Armored Avenger left out of the decade's biggest crossover event entirely. Comics are a product of their time, as are the heroes within the stories. If Iron Man can rise so suddenly, it makes one wonder which C-list superhero will become popular next.