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Samson was, at one point, a good templar. Knight-Commander Guylian personally gave him his templar shield. He claimed that he left the Templar Order because he helped some apostate mages escape, but in fact he was dismissed because Meredith Stannard caught him delivering messages between a mage named Maddox and his lover.
Dragon Age: Inquisition
He was one of the first of the high-ranked Templars infected with Red Lyrium and knew Corypheus's goals. He willingly infected his templar subordinates with Red Lyrium knowing that he was rotting their minds and warping their bodies.
If the inquisition recruits the Mages, then Samson leads the assault on Village of Haven with Corypheus standing beside him. After his master wins the battle and Samson receives from him new missions to fulfill.
Samson created a red lyrium armor that feels like drowning in fire when he first donned it, and by enduring it he had become fit to be "The Vessel".
Samson accompanies Corypheus to the Arbor Wilds in search of the Well of Sorrows. After fighting through the ancient elven guardians, Samson comes to close to the Well when he is confronted by the Inquisitor. Samson reveals that he will drink from the Well, becoming "The Vessel" of its knowledge for Corypheus. The Inquisitor defeated Samson and took him prisoner for judgement back to Skyhold.
When brought for judgement he defends his actions as merely feeding his men the same lies that the Chantry fed both him and them during their time with the Templar Order: "Hope instead of Despair" and "pain for purpose". Samson believed that templars have always been used and that he was providing the Templar Order a mercy by having them go out in a blaze of glory instead of letting them be thrown away by the Chantry as soon as the lyrium destroyed their minds. He's wanted for his actions in Kirkwall and Orlais. The Inquisitor has the options of:
- Handing him over to Kirkwall.
- Exiling to the Wilderness.
- Having Arcanist Dagna study him.
- Conscript him under Cullen.
- Or simply locking him in a hole.