Meros

Meros was a Baalite apothecary of the Blood Angels’ Ninth Company who accepted a daemon’s bargain on Signus Prime and became the Red Angel. He entered the bargain so that Sanguinius, primarch of the Blood Angels, would not be required to do so.

Before accepting the bargain, Meros removed his own gene-seed, the organs that preserve a Space Marine’s hereditary line. This was the last surgical act he performed as an apothecary, and it marked the point after which the Ninth Company could no longer regard him as a battle-brother without hesitation. The Ragefire then took the remainder of him. The being that left the cathedral was the Red Angel, which wore a loyalist’s face and embodied what Sanguinius had himself been tempted to become. The victory at Signus Prime was secured at a cost greater than any Baal had previously paid.

Meros did not remain a Blood Angel except in a residual sense. The daemon that used him retained his name. Baal continues to claim the apothecary, while the warp claims the Angel. Each account is accurate as far as it goes, since both concern the same individual, but neither claim allows the other to share the body.