Formerly a decorated hero in the First War, Diodor the Damned studied necromancy and eventually became one of the first members of the Cult of the Damned. After leading two successful assaults against the Scarlet Monastery, he was killed when the crusaders figured out his plans and fought back the third (and final) assault.

Diodor is mentioned in the Compendium of Fallen Heroes found in Acherus, and is considered a hero by the Scourge.