While Venom might be one of Spider-Man's most famous villains, he's fought plenty of other heroes too. Back in the 1990s, Marvel pitted the Lethal Protector against the Juggernaut, Wolverine, Ghost Rider, and even Superman. But long before Venom was one of Marvel's biggest draws, the symbiote hero fought another hero that no normal hero could ever subdue: the Incredible Hulk.
In one of the stranger corners of the Marvel Multiverse, one What If...? story saw the symbiote bond with the Hulk and consuming it. It remains one of the most bizarre things the Venom symbiote has ever accomplished, even though very few people ever reference it when referring back to Venom's heights as an adversary in the Marvel Universe.
WHAT IF VENOM TOOK OVER THE HULK?
The story appears in 1989;s What If...? #4, by Danny Fingeroth and Mark Bagley, which asked the question "What If the alien costume had possessed Spider-Man?"
The story recaps the events that led up to Peter Parker casting off the alien costume in the Marvel Universe For this alternate timeline, the diverging point comes shorty after Spidey returns from the Beyonder's planet after the events of Secret Wars. Spider-Man learns his suit is alive, and Reed tries to blast it off with the Sonic Blaster, but the symbiote doesn't leave Parker's body. It's already bonded with him. As the Fantastic Four try to remove the symbiote, the alien overtakes Peter's mind, trying to escape.
Unable to divide Peter, the heroes call in Doctor Strange to help, but even the Master of Mysticism can't get the alien off Peter. All of this leads to Peter and the symbiote becoming inextricably attached, culminating in Venom breaking free and escaping.
HOW VENOM BONDED WITH THE HULK
After Spider-Man goes missing for days, the Hulk, however, is seen pummelling New York, forcing Thor to try to subdue him. Doctor Strange arrives on the scene, and rightfully assesses that the Hulk is far too out of control to be responsible for his actions. So he opens up a portal for the Hulk to enter where he can't hurt anything until he calms down and is ready to leave.
Before he can tumble into the dimensional rift, however, Spider-Man swings in and pulls the Hulk out. He kicks Doctor Strange to the ground and turns on the Hulk. The symbiote leaves Spider-Man, dismissing his shriveled, dying body, as Venom covers Hulk completely. The Venom personality takes over, leaping away with his now unlimited source of power.
HOW VENOM ATE THE HULK
In a twist that would be later recycled in both the main comics (in The Hunger storyline) and the Venom film, the symbiote consumes life-energy, feasting on vitality until it can be cast-off to another host. Peter Parker, who has been prematurely aged beyond recognition, has enough time to visit Aunt May before returning to the Baxter Building to die of old age. Before dying, Peter created a device, based on Reed's notes and his own biological data, which could both track the Hulk-Venom and destroy him.
The Avengers track Venom to Mount Rushmore, where they set out to find Venom. When they find him, he seems genuinely remorseful but admits he has achieved "true symbiosis" with the Hulk, meaning he might not hurt the gamma-infused monster. Still, Thor tries to apprehend him, and Venom, refusing to be imprisoned again, retaliates, managing to knock down Thor.
In the biggest twist, Thor finally removes the symbiote from Hulk's body, revealing Banner alive and well. As Thor notes, the symbiote was telling the truth. While it did indeed leave Banner unaffected by taking over his body, it completely consumed at the physical manifestation of The Incredible Hulk, presumably by eating away at all of the gamma radiation and extra flesh produced in Banner's transformation. This continues to be almost unheard of in the comics, especially as Hulk has a healing factor on par with Wolverine's.
It remains unclear, given the brevity of the story, whether Venom also cured Banner of the Hulk's mentality. After all, the Jade Giant is another personality. However, the Venom symbiote absolutely devoured the Hulk's body, seemingly permanently. It also made the alien costume strong enough to attack and overwhelm Thor later in the issue, before finally being subdued by Black Bolt and killed by a vengeful Black Cat.
However, Venom latches onto Thor, hoping to consume the God of Thunder himself as his new Host. This eventually leads to a confrontation with Black Bolt and the final death of the Venom symbiote. But before it was defeated, it did what not many others have been able to do -- kill the Hulk for good.