Erud Vahn was a Techmarine of the Death Guard during the Great Crusade. One of the foremost "Forge Tyrants" of his Legion, he was a master of alchemic warfare and spent long years studying on Mars. When Mortarion declared for Horus at the start of the Horus Heresy, Vahn found himself more closely aligned with the Mechanicum and remained loyal. Vahn renounced his legion, becoming a Blackshield in a unit under Endryd Haar. Serving as Haar's second in command, Vahn fought in the Xana Incursion.