Erebus

Meet the man more or less responsible for the crap place the Imperium became.

What a bastard.

Don't you want to punch his smug face?

Erebus was a Dark Apostle of the Word Bearers and one of Lorgar's trusted lieutenants. During a certain time, he become a devout servant of Chaos and co-conspired with Kor Phaeron in order to bring the downfall of the Imperium. Though, to Erebus' credit, whilst Kor Phaeron was able to corrupt his Primarch, it was he who was indirectly responsible for the Horus Heresy. For it was he who had corrupted Horus, and he, along with Horus, masterminded the drop site massacre of Isstvan V. He continued to serve Horus as his spiritual advisor until his defeat in the hands of the Emperor (though Horus did cut Erebus' face off after Erebus threw a hissy fit when Horus changed Erebus' plans to turn Sanguinius to Chaos). After Lorgar's merry little crusade to turn Angron into a RAGE-fulled Daemon Primach, Kharn challenged Erebus to a duel after Erebus teamkilled Argel Tal MURDERED HIS LAST FRIEND. Erebus had the crap beaten out of him EVER LOVING SHIT BEAT OUT OF HIM AS THE ENTIRE WORLD EATER LEGION LET OUT A COLLECTIVE "DAAAAAAAAAAAMN" , but escaped.

Erebus currently holds a position in Lorgar's Dark Council, toying around with Kor Phaeron. He showed up in the 13th Black Crusade to sacrifice a million innocents to the gods of Chaos, and then, having apparently fulfilled his contract and knowing they were going to fail once more, took his warriors and got the hell out of there. He has shown notable distaste for Abaddon's status as Warmaster of Chaos, believing that a new Warmaster is needed. Which goes to show that just because you've spent ten thousand years chilling in the Eye of Terror doesn't mean that you forfeit common sense.

Also, even if you knew nothing about the Heresy, Chaos or the 40k setting generally and just got handed a copy of the first couple of books you'd still realize that Erebus is corrupting the living fuck out of everyone, via the venerable 'Rasputin Maneuver'. The fact that he spends all his time just chilling out with no-one else from his legion, constantly being complained about but Horus just says 'Nah he's cool' pretty much proves that no-one else in the setting has even the vaguest ability to connect obviously connected facts. He's a slippery, creepy motherfucker and if anyone (looking at YOU Loken) had an ounce of sense they'd have tossed him out a fucking airlock the second they set eyes on him.

His name is based on the Greek entity Erebus, who was the son of Chaos. And it quite suits him since he is a Chaos Space Marine, and the very first one to boot.