Horus: Horus was a great military commander in the early years of the Imperium, and was given the highly honoured title of Imperial Warmaster.
Before travelling back to Terra to accept his new title, Horus was taken ill on a feral world, where he was introduced to a warrior cult. Although the Imperium approved the joining of these cults to aid recruitment through the power of the "warrior brother from the stars", this cult proved to be Horus' undoing. When he left he had been possessed by a Demon and the change of character was obvious.
When Horus was recalled to fight in the Imperial Crusade he recreated the lodges of the warrior cults in the legions and Orders of the Adeptus Mechanicus under his command.
Horus was later sent to return Istavaan III to Imperial control following its declaration of independance, the Emperor was unaware of his disloyalty. Horus destroyed the planet, but left a single frigate of loyal troops to escape with a warning to the Imperium.
Once the First Inter-Legionary War approached Terra and the traitor legions of Horus captured the Outer Palace, the Emperor disconnected himself from the Astronomican and teleported to Horus' battle barge with a company of Custodes Adeptus and Imperial Fists. Horus was killed in the fight that left the Emperor seriously wounded, but some reports say his corpse was never found.
Horus was the primarch of the Lunar Wolves chapter, who later became known as the Sons of Horus. It was under this name that they began the Horus Heresy, but were then driven into exile. With their Warmaster lost to them, some say he was taken and cloned, the Sons of Horus rejected his name and became the Black Legion, painting their armour black and exiling themselves further
Source: Unknown by unknown
Submitter: IBBoard
Hive World Terra