How did Marvel Zombies undead infection start in the comics?

The infection in Marvel Zombies is a gruesome affair, but its origins are a convoluted mystery involving a founding Avenger and a paradox.

Marvel Zombies seems novel now, but it was something truly landmark at the time. The debut story, Crossover, had all the hallmarks of a major event in the making. 

A large part of that is the surprise of the Zombies. The story is presented initially not as a horror event but as the first crossover of the Ultimate and 616 universes, as Ultimate Fantastic Four’s Reed Richards receives a message that he thinks is coming from 616 Reed. 

It’s all a scheme by the Zombies to get fresh humans into the world to feast on. The zombie infection is already in full swing by the start of Crossover, but how did it start in the universe? 

The first Marvel Zombie is Sentry or Giant-Man, depending on perspective

The actual origin of the Zombie virus is never revealed, but the Marvel Zombies infection associated with the original Ultimate Fantastic Four story starts with The Sentry. How The Sentry got infected in the first place is a bootstrap paradox.

In Ultimate Fantastic Four #22, we learn Sentry fell from the sky, infected and zombified already. He turns the heroes around him, and in less than 24 hours, Earth is a wasteland of corpses and zombies, with but a few straggling human survivors who don’t last long. 

Many of the heroes don’t handle the zombie transformation well, their normal personalities showing through when their hunger is sated. However, a few heroes, such as Hank Pym, aka Giant-Man, relished the zombie turn. Various efforts to find food sources culminate in the Marvel Zombies consuming Galactus and gaining some of his Power Cosmic, which enables Pym to travel to another world. 

On this other world, Pym infects the Inhumans, who in turn infect The Hulk as he returns from Sakaar. The infected Hulk rampages on Earth, leading to the Sentry being dispatched to stop him. Hulk baits Sentry into transforming into his human form and then bites him. 

With no means of defeating The Sentry, even as a zombie, the decision is made to send him through time. He’s sent back to his Earth years in the past, where he creates the original zombie infection, effectively closing the loop on the zombies so that the virus cannot escape itself.

This seems to make the actual canon that Giant-Man started the Marvel Zombies outbreak, as he would be the earliest infected in the timeline. However, he could only start this after The Sentry had turned him later in his timeline — hence, the bootstrap paradox. 

What originally created the Marvel Zombies infection to necessitate this has never been revealed. We have, however, seen multiple alternate takes on how the zombies were created, such as an alternate Earth’s Squadron Supreme becoming zombies after a failed experiment. 

With Disney+’s Marvel Zombies dropping in 2024, it seems likely that we’ll get yet another explanation soon enough. 

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