Warhammer 93k

Whaddaya know: someone involved in creating The Dark Future of Warhammer 40,000 is evidently a Thelemite.

Perturabo

When the twenty infant Primarchs were spread across the galaxy by the forces of Chaos, the young child who would become known as Perturabo was discovered on Olympia, climbing the sheer cliffs below the city-state of Lochos. The city guard brought the child before the Tyrant of Lochos, Dammekos. Intrigued by this child, Dammekos adopted him into his family.

Perturabo never trusted the Olympians and, although Dammekos took time and trouble to win the trust and affection of the boy, Perturabo never responded with any warmth. Many saw him as a dark skinned,cold youth, dark and melancholy, but with a mind like a razor. ....

The Horus Heresy

In the midst of the cleansing of the Hrud Warrens on Gugann, matters were brought to a head. It was Warmaster Horus himself who broke the news to Perturabo that Olympia was in rebellion. Dammekos had died and the population had taken up arms. Perturabo was by this time tired of repeatedly having to prove his worth, and the thought of being the only Legion unable to hold its own homeworld appalled him. Horus bade Perturabo to return to his place of discovery ....

Maybe a cranky ex-Thelemite Chaoate?

Beliefs

....
They see themselves as titans of old who are loose in the universe, doing whatever they like, knowing that no natural nor man-made law can stop them. They honour the Chaos gods as a pantheon but are not truly devout themselves. Their greatest loyalty is to their daemonic, semi-deified Primarch, Perturabo, who they believe saved them from being sacrificed by the Emperor.

Battle-cry

“Iron Within, Iron Without!”

A monotone chant of “Iron Within, Iron Without” is repeated during the beginning of combat operations.

Saying “Iron Within” to elicit the response “Iron Without” is sometimes used by Iron Warriors to identify each other, especially in confused combat, such as that in tunnels or during combined operations with other Chaos forces.
....
When the Iron Warriors turned to Chaos, this symbol was slightly redesigned, and is now superimposed over the symbol of the eight-pointed Chaos star.

Can someone who knows more about Warhammer 40k help me out here?

And while we're here: In The Grim Future of Hello Kitty There Is Only War