Background on WorldWarHulk: PlanetHulk

In the 2006 storyline "Planet Hulk" by Greg Pak, after the Hulk destroys much of Las Vegas, a secret group of superheroes called the Illuminati trap the Hulk and rocket him into space to live a peaceful existence on a planet uninhabited by intelligent life. After a trajectory malfunction, the Hulk travels through a wormhole and crashes on the violent planet Sakaar. Weakened by his journey, the Hulk is captured, then sold as a slave. In a gladiatorial arena, he makes a deadly enemy by scarring the emperor's face. The Hulk overcomes great odds to become a gladiator, a rebel leader and eventually a king.

The Hulk's kingdom is in the process of making treaties with all the factions on the planet, lifelong enemies are now becoming allies and the Hulk is content. The peace does not last long. The shuttle which carried Hulk to Sakaar malfunctions, causing a massive explosion, killing thousands, including his spouse and queen, Caiera, and their unborn child. The explosion fractures the planet's tectonic plates leading to their eventual disintegration, killing almost everyone on the planet.