Angron

The ANGRIEST son of a bitch in the galaxy. He was so angry that the part of him that was angry exploded from his head, thus making him permanently angry. Being kidnapped by the Emperor didn't help matters so he fucking RAGED at his dad by joining up with Khorne, God of FUCKING BATTLE RAGE AND REGULAR RAAAAAGE!!!. Among his exploits include single handedly slaughtering the entire population of a planet within a night. Must have been pretty high that night. Also slaughtered a whole contingent of Eldar and a Farseer in his sleep. Oh yeah, and he was also a Gladiator and the leader of a rag tab group of Gladiator rebels who slaughtered hundreds of armies. One at a time of course, they lost as soon as 7 massive ones came after them all at once, of course the fact that they hadn't eaten anything since they escaped probably contributed to this. Angron began to RAAAAAAGE at the Emprah after he saved him from this fight.

Oh yeah, and he was lobotomized long ago so he finds joy only killing shit. Replicated this technolog on his fellow legionaries. In spite of this that swell guy became Angro's 'cool head'. Ironic.

Primarch of the World Eaters and that swell guy.