Sanguinius

Sanguinius is the Primarch of the Blood Angels chapter.

Though not first in favor among the Emprah's primarchs (that position belonged to Horus, pre-heresy), he was first in power. Of the canonical Space Marines, his chapter is the most batshit-loyal to the Emperor.

He is dead. Oh boy is he ever dead. When the Emperor went with his forces to defeat Horus during the Heresy, Sanguinius got sequestered from the greater force and forced to fight Horus alone. Though Sanguinius was the most powerful of the primarchs, Horus had received the backing of all four chaos gods, and so he slew Sanguinius so hard it mind-fucked his entire chapter. Nowadays, all Blood Angels have to cope with the Red Thirst. Succumbing to the Thirst leads to the Black Rage.