Angron Thal'kyr, also known as Lord of the Red Sands, Child of the Mountain, and the Red Angel, is the primarch of the World Eaters in Warhammer 40,000.
Landing on Nuceria as a child, he slaughtered a group of Eldar before being found by slavers. Once taken captive, he was sold to the highhest bidder, that being the House of Thal'kyr. He would live his youth fighting his way through the gladiator pits of Desh'ea, the capital city of the planet, raised under the care of fellow gladiator Onoemaeus. When he refused to fight the one he saw as a father later in life, his reward for his defiance came in the form of the Butcher's Nails, an arcane technology from the Dark Age of Technology that rewarded only slaughter and muffled all other emotions with spikes that go directly into the recipient's brain. One day, he would stage a revolt that saw his fellow gladiators fight their way out of the arena and into the streets, where he and his rebel-kin would refer to themselves as "The Eaters of Cities".
Their revolt would last until they were cornered on the Desh'elika Ridge. They swore to make their final stand, but the Emperor of Mankind stole Angron away, preventing his death. This enraged him, and the legion that stood before him bore his fury until Kharn, the first captain, calmed him down and explained that he were to be the primarch of the XIIth Legion, formerly the War Hounds. All the while, the Nails continued to eat away at him, slowly killing him. He refused to fully accept his legion, even abandoning them at one point before being convinced to join back when all of the Legion would take the Butcher's Nails.
Some would not survive the surgeries, but when the Nails were implemented upon the now renamed World Eaters, they changed for the worse. The Legion once known for their brotherhood and comradery devolved into screaming, bloodthirsty maniacs. One campaign for them sealed their fate when Lorgar Aurelian, primarch of the Word Bearers, enacted a ritual to infuse the power of Khorne; the Chaos god of blood, war, murder and slaughter; into Angron, thus completing his ascension into a Daemon Prince.
He partook in the Horus Heresy by engaging in a great battle with Sanguinius during the Siege of Terra, ultimately resulting in his defeat and banishment to the Warp. Since then, he has returned to the material realm many times, being very active in his quest to claim skulls and spill blood in the name of his master, for he was never meant to be free, only a slave, now and forever.