Sanguinius was one of the Primarchs created by the immortal Emperor of Mankind. He founded the Blood Angels chapter. He was killed attempting to defend the Emperor from Horus during the great betrayal of the Heresy.
After the Primarchs were scattered to the corners of the galaxy by the fell powers of Chaos, Sanguinius came to land on the second moon of Baal. There the infant Primarch was discovered by one of the wandering tribes of humans who called themselves the Folk of Pure Blood, or more simply, the Blood. Sanguinius's life nearly came to an end there and then, as the touch of Chaos had altered him. Small vestigial wings, akin to those of an angel, protruded from his back. Many were those who wanted to kill the child as a mutant, while others wanted to spare the boy, for in every other way, he was as perfect a child as ever seen. Eventually humanity prevailed and the child was spared.
Sanguinius grew quickly and learned everything his parents could teach him. After three weeks he was as large as a three year old child, and could walk. As he grew his wings grew also, changing into mighty pinions that could bare him aloft on the desert air. By this time he was one year old, he looked and acted like a man in his youthful prime. He could walk without a rad-suit in the poison desert, and could shatter mighty boulders with a single blow.
When a wandering band of mutants surprised the tribe, Sanguinius slew them all, although they numbered over a hundred. This was the first time the members of the Blood had ever seen him truly angry, for he felt his comrades' lives were in danger. When the blood-rage overtook him he was indeed terrible to behold. His full primarch powers came upon him and a nimbus of light played about his head.
Sanguinius distinguished himself in the fateful years that followed. He soon rose to leadership of the Blood, and under his guidance they rolled back the mutant tide. For a time Mankind had a breathing space on the moon called Baal Secundus. Sanguinius was worshiped as a god by his followers.
It was shortly after that fate intervened once more. The Emperor had searching across the galaxy for his lost children and his incredible psychic powers led him to Baal. His ship landed at the conclave of the Blood and he walked straight to the home vehicle of Sanguinius.
Others among the Primarchs are said to have fought against the Emperor when they first met but this was not the case with Sanguinius. He immediately recognised the Emperor for who he truly was and bent his knee before the Lord of Mankind. The Emperor raised him up and looked upon his people and saw they were fair and noble. The best of the warriors were to become Space Marines, using the gene-seed extracted from Sanguinius, the rest were to defend mankind's birthright upon Baal Secundus.
Thus were born the Blood Angels, among the chapters of the first founding. They joined the Emperor's fleet and sailed across the Sea of Stars to participate in the Great Crusade.
Sanguinius distinguished himself during the siege of Earth, when it looked as if the Imperial Palace and the entire home world might fall under the iron heel of Chaos. He organised the final defence of the Emperor's Palace, he slew a giant Bloodthirster of Khorne single-handedly and held the Ultimate Gate alone when all others had fled. When the Emperor teleported aboard Horus's battle-barge for his final confrontation with the rebel warmaster, Sanguinius was there also.Battle raged throughout the daemon-infested spacecraft, and Sanguinius became separated from the Emperor. While he was still alone he chanced upon Horus and , although bearing the wounds of his earlier actions, knowing it would almost certainly spell his doom, he immediately attacked the Warmaster. But Sanguinius was no match for Horus at the height of his daemon-provided power, and was slain by the Warmaster with contemptuous ease. Knowing he was no match for Horus, he sacrificed himself in a final attack. His sword piercing the Warmaster's armor as Sanguinius fell into the lightning claws of his foe. This tiny hole allowed the Emperor to deliver the final blow against Horus. Sanguinius' sacrifice saved humanity. The psychic echo of his death can still be heard by the Blood Angels, causing a madness and a fury to come upon them as they see dark visions of their Primarch's final hours.
To this day, the Blood Angels are among the most feared and least trusted of all Space Marine Chapters, souls haunted by the horror of those ancient events and whose bodies are wracked by a secret and terrible thirst that must never be revealed.