Horus Lupercal - The Traitor || Warhammer 40K Lore
49Horus Lupercal was one of the 21 Primarchs created by the Emperor in the earliest days of the Imperium, just after the end of the Age of Strife. Like the other Primarchs, Horus was scattered from Terra by the Gods of Chaos and was placed on a far-away world in an attempt to prevent the coming of the Age of the Imperium. Traditional accounts state that Horus was the first Primarch to be rediscovered, fighting alongside his father in the Great Crusade as Lord of the Luna Wolves. Becoming the favored son of the Emperor and beloved by most of his brother Primarchs, Horus eventually rose to become Warmaster of the Great Crusade and was seen as second only to the Emperor himself in power and prestige. But in spite of all of this, he was eventually corrupted by the powers of Chaos and initiated the Horus Heresy against the very Imperium he helped create.
https://wh40k.lexicanum.com/wiki/Horus_Lupercal