Kaldor Draigo

Kaldor Draigo is the Supreme Grand Master of the Grey Knights and a warrior beyond reckoning. As a lowly Battle-Brother he banished the Daemon Prince M'kar the Reborn and he has risen steadily through the ranks to become the Grand Master of the most secretive Chapter of Space Marines. Yet ever since his battle with M'kar, Draigo has been cursed to a life within the Warp, doomed to walk within the Realm of Chaos. To remain pure when constantly assailed by Chaos shows such fortitude and personal strength that it is beyond measure. But while Draigo lives, he will prevail and one day, he will return.

Kaldor Draigo is famous for killing a daemon prince in his first combat action, banishing daemon primarch Mortarion back to the warp, somehow carving the name of the previous supreme grand master Janus into the heart of said daemon primarch, single handedly holding off a daemon horde for two days in real space, killing a daemon prince with a broken sword, Killing one of Khorne's strongest bloodthirsters with little to no weaponry, taking said bloodthirsters axe and reforging it into a sword for his own personal use USING HIS MIND, slaying 6 of Slaanesh's chosen daemonettes, setting fire to Nurgle's garden, walking into the City of Tzeentch and single handedly smashing it to ruble and slaying countless daemons whilst being trapped in warpspace. Yeah, he's a fucking troll....

The Emperror himself, looking at his deeds, stood up... And quit his fucking job because clearly this Draigo asshole made him irrelevant.

tl;dr

BECAUSE GW WOULDN'T LET MATT WARD BRING BACK ROBOUTE GUILLIMAN