Zombies have a bad habit of showing up to take a bite out of the Marvel Universe, but the scourge of the undead heroes wasn’t born in a vacuum. Marvel’s zombies trace their origins in print to a three-part story arc from 2005’s Ultimate Fantastic Four that played heavily into the reality-jumping technology of Mr. Fantastic.
Starting in Ultimate Fantastic Four #21, the first issue to kick off the run with the creative team of Mark Millar and Greg Land, Reed Richards makes contact with an alternate dimension version of himself in the "Crossover" storyline. Though their history was fleshed out extensively in later storylines, this was the first time we got a glimpse of the rotten universe of the Marvel Zombies.
Using a teleporter device to cross over and meet his alternate self for coffee, Reed soon comes to realize he’s been had, and his other self isn’t the cool guy he thought he was at all. The zombified Fantastic Four set up the meeting because their world, Earth-2149, is overrun with the zombie plague called the Hunger virus -- and they’re running out of food.
According to zombie Reed, Earth-2149 was once very much like the “normal” world. But a zombified version of Sentry literally punched his way from another dimension to this one in search of food. Though it's not explained at the time, the Marvel Zombies Return storyline later reveals a Watcher sent Sentry to this world and allows this story to play out infinitely on a time loop as a way to contain the virus. In this world, the Avengers were the first to fall because they were the first to respond. The virus specifically targeted superheroes first and spread outward from there. The entire world was overrun in just 24 hours thanks to zombie Quicksilver spreading the plague, which then allowed super beings to devour normal humans.
Seeking more food, zombie Reed, who retains his mental faculties, tricks Ultimate Reed and opens the path between dimensions solely to get a new food source. Reed is only able to escape the clutches of his hungry doppelganger, as well as a ravenous zombie Hulk, with the aid of Magneto.
As one of the few uninfected left, Magneto has been keeping others at bay with his powers. He needs Reed’s help to save other uninfected, including a young girl, from the zombies. At the same time, the zombie Fantastic Four are not waiting around for Reed. They use the teleporter to head to Earth-1610 where the Ultimate Fantastic Four meet them and trap them after a brief skirmish.
In the zombie dimension, the Fantastic Four and Magneto team up to take on the likes of zombie Wolverine and Thor. Thing also gets a chance to go toe-to-toe with zombie Hulk. The team comes out victorious, and they make their way to the decrepit Baxter Building and the teleporter device. It’s here the team returns to Earth-1610, and Magneto sacrifices himself to destroy the teleporter so the others can’t follow. This quarantines the threat for a time. However, knowledge of other dimensions keeps the zombies going as they attempt to invade other realities and, in many cases, they succeed at doing so in later storylines.
While this was only one brief run in 2005, the zombies have been fan favorites, and their lore has been expanded considerably over many miniseries since then, including 2019's Marvel Zombies: Resurrection, which published one issue before suffering delays related to the coronavirus (COVID-19) pandemic. But later this year, Marvel will once more have to deal with its zombie problem.