Prior to the Galactic War, Tagriss betrayed the Empire to serve under the rogue Dread Masters. The six granted him the title of Dread Lord as a reward. Shortly before the demise of Dread Master Styrak on Darvannis, Lord Tagriss was dispatched to an Imperial station known as Arcanum, home to the collection of Sith Artifacts and technology gathered by the Emperor himself. Accompanied by a force of Dread Host soldiers, Tagriss was to obtain the Seeds of Rage, terraforming devices created by the Sith alchemist Lord Fulminiss.
Following the Dread Lord's success, the Seeds were launched to planets across the galaxy. Later, Tagriss and his forces returned to Arcanum, where the former claimed the ancient Darkstaff, before fleeing to a Dread Guard sanctum on Belsavis. An Imperial strike force assembled by Darth Acina of the Dark Council tracked Tagriss there, only to find the traitor's apprentice, Dread Guardsman Avarok. Following the Pureblood Sith's failure to eliminate the Imperials, Tagriss killed him as punishment.
On Ilum, Tagriss ventured to an abandoned Jedi Temple, corrupting it with the final Seed of Rage. Utilizing the temple's lightsaber forge, he sought to claim its power as his own. Unfortunately, the Imperials had torn through the former's corrupted Dread Host, and interrupted his ritual to construct a piece of armor from the Seed. Enraged, Tagriss attacked the intruders, only to be defeated. The Seeds of Rage stolen by Lord Tagriss would become the origin of Dread Master Bestia's own terraforming devices, the Dread Seeds.
- It is also possible that Lord Tagriss was corrupted by the Dread Masters, and forced to serve, but his statement, "I will claim the Seeds' power and no one will stop me," suggests he joined them willingly.
- A rare collection of armor, the War Hero Vindicator set, includes a torso piece identical to that of Lord Tagriss.