The etymology of "Ahriman"

The destructive spirit...

Ahzek Ahriman is an eponymous villain in the Warhammer 40K universe. A seeker of forbidden knowledge, traitor to his legion and Primarch, and pawn of Tzeentch, he is most famous for casting his Rubric which turned the Thousand Sons into mindless automaton.  

During the Great Crusade, his origin story is told in Graham McNeill's amazing Horus Heresy novel, "A Thousand Sons".  We learn that Ahriman was born on Terra and once had a twin brother Ormuhzd who died from the Flesh Change curse that eventually led to the Thousand Sons' damnation.  

If you haven't read this yet, go do so...NOW!

Given the mystic penchant of the Thousand Sons, it's no surprise that Ahriman's name has quite the philosophical origin.  Enter Angra Mainyu, a.k.a. - Ahriman.

Cheerful looking guy ain't he?

In Zoroastrianism, Ahriman is the "destructive spirit".  He created a horde of demons who embody envy, greed, and wrath.  In modern Zoroastrianism, he is described as an allegorical personification of humanity's evil tendencies.  

In Warhammer 40K terms, that's pretty on-par with Ahry's tendencies.  He raises up cults of forbidden knowledge only to plunder them when he gets what he wants. He is searching for the Black Library so he can become the galaxy's ultimate bookworm.  

So where does Ahriman's brother, Ormuhzd, fit in?  

"I've got a flying machine!"

To understand Ahriman, you first need to know a little bit about the Zoroastrian pantheon.  Zoroastrianism is a pre-Islamic religion of Iran from around the 5th or 6th century BCE.  The ruling deity, Ahura Mazda (Ormizd or Ormazd), was a being of the highest worship in Zoroastrianism.  It is one of the most ancient religions of the world that combined "a cosmogonic dualism and eschatological monotheism in a manner unique [...] among the major religions of the world" (wikipedia).

Ahura Mazda created twin serpents, Angra Mainyu (Ahriman) and Spenta Mainyu (an aspect of Ormizd).  Where Angra Mainyu represented greed, wrath, and envy, Spenta Mainyu was created as the antithesis of Ahriman.

So it's not a great leap of logic to see where the author drew inspiration when writing Ahriman's origin story in "A Thousand Sons".  Where Ormuhzd the Legionary died, the diametric balance the twins gave one another was lost and thus put Ahriman on a path that would last 10,000 years long. 

Now that we see his Primarch has brought him back into his cabal of sorcerers, it'll be interesting to find out what Tzeentch is planning next for his arch-sorcerer.