Mordecai Toth

Mordecai Toth was the Inquisitor dispatched by the Ordo Malleus to the Civilised World of Tartarus to warn the Blood Ravens Chapter about the Warp storm that was about to hit the planet and to ensure that the forces of Chaos operating on that doomed world were found and purged.

Toth initially suspected the Blood Ravens' Force Commander on Tartarus, Captain Gabriel Angelos of the 3rd Company, of being tainted by the Ruinous Powers due to the commander's stubborn refusal to flee in the face of the arrival of Chaos forces from the Alpha Legion on the planet, which Toth perceived to be a symptom of Angelos becoming overly obsessed and enamoured with Chaos. He did not suspect the true Traitor, the Blood Ravens' Librarian Isador Akios, until it was too late.

Toth helped the Blood Ravens purge the forces of Chaos from Tartarus and even gave Gabriel his Daemonhammer -- Godsplitter, which had been forged from a fragment of a Craftworld Aeldari Avatar of Khaine's sword. It was with this same weapon that Captain Angelos, in an attempt to destroy the artefact of Chaos found on the world called the Maledictum, unintentionally released a powerful Greater Daemon of Khorne from its prison within the object where it had been trapped following a battle with the Asuryani of the Biel-Tan craftworld for many millennia.

During the course of the Blood Ravens' campaign on Tartarus, it was discovered that Inquisitor Toth had actually been present on the planet before the initial Ork invasion that had called the Space Marines to the world; presumably Toth was there trying to find the Maledictum before it could fall into the hands of the servants of Chaos.

Sources

Dawn of War (Novel) by C.S. Goto
Warhammer 40,000: Dawn of War (PC Game)