Thanos Is Hulk's Ultimate Nemesis, And He Doesn't Even Know It
While 2009's World War Hulk had a tragic ending that saw the Hulk learning the truth about why his family was killed, he's probably still in the dark about the secret involvement of Thanos. In the classic storyline where Hulk returns to Earth after liberating the planet Sakaar and suffering through its subsequent destruction, the Jade Giant comes to believe that the Illuminati (Iron Man, Mr. Fantastic, Doctor Strange, and Black Bolt) are responsible for the deaths of his family. In truth, it is eventually revealed that one of his own allies was responsible. However, what drove one of Hulk's Warbound to betray him in the first place? Marvel Comics would reveal nearly a decade later that it was because of Thanos, the Mad Titan himself.
A journey that began with Planet Hulk from writer Greg Pak, the Illuminati make the unilateral decision to send Bruce Banner's Hulk into space. They believe that he's caused too much damage to the world and can never be controlled, and that he will always exist as a major threat. Crashlanding on the world of Sakaar, Hulk becomes a gladiator, eventually gaining allies known as the Warbound and liberating the world of its oppressive Red King. Taking the throne for himself, Hulk eventually starts a family. However, the same ship that sent Hulk to his happy ending takes it all away when its warp drive self-destructs, resulting in the death of his wife and millions more. Swearing revenge, Hulk returns to Earth convinced that the Illuminati are responsible in World War Hulk.
However, it is eventually revealed that the ship's explosion was caused by the Red King and his followers. Furthermore, Hulk's ally Miek knew about it and said nothing, knowing that Hulk would abandon the peace they fought for and would be on the warpath once again. An active seeker of war, Miek is held responsible for the millions who died and the widespread devastation the explosion caused. While the insectoid warrior admits that he wanted Hulk to "never stop making them pay" due to his species having gone extinct during Planet Hulk, it wouldn't be until 2019's Thanos #3 from Tini Howard and Ariel Olivetti that it is revealed why Miek's race was so endangered to begin with. While the Red King likely played a large role, this issue reveals that Thanos and his forces continually attacked the Sakaaran insectoid race multiple times years prior, satisfying the Mad Titan's desire to kill and feed his bloodlust. As such, Thanos's massacre reverberated through time, resulting in Hulk losing his adopted world and his family (though Banner likely has no idea).
From Thanos to the Red King to Miek, this is a truly dark domino effect that proves the Mad Titan is ultimately responsible for Hulk's pain, unintentionally causing the loss of his world, his wife, the banishment of his sons, and ultimately what was his best chance to lead a life of peace. It's also possible that Thanos has no idea what he caused either, though he'd likely relish the discovery if it were ever made known to him. In contrast, Hulk has a darkly personal reason to go after and hunt down the Mad Titan...if he only knew what Thanos did years before the Illuminati sent him to space.
This narrative thread and secret Thanos prequel to World War Hulk is something that could easily be missed by even the biggest Hulk fans. All the same, it certainly shines a whole new light on the iconic stories written by Pak. While Hulk's ally Miek bears the blame for Sakaar's destruction and the death of Hulk's wife, it's likely that he never would have been so dark and vengeful had his race not been endangered and ultimately driven extinct in a mass slaughter that began with Thanos himself.