Before succumbing to the temptations of the Darkness, Yor was a Guardian known as Rezyl Azzir. Rezyl was a noble man, beloved by the people and celebrated as a beacon of hope against the forces that would destroy mankind.1 At some point he traveled to the Moon, chasing rumors of nightmares, and encountered the Hive. Leaving his Ghost at the door, he began fighting his way through the Hive tunnels and eventually killed a Knight who was Xyor’s betrothed.2 When he returned to the surface, he brought trophies with him and affixed them to his hand cannon, Rose.3
The exact process Rezyl underwent is unknown. Over time his fears and his pride led him to want more. Whispers from the Darkness slowly grew into a voice, seducing him with promises of power and glory. Eventually, he turned away from the Light,abandoned his old persona entirely and he adopted his new name, “Dredgen Yor” (which in an old language means "The Eternal Abyss"4).
At some point Yor visited the town of Palamon, where he first encountered Shin Malphur. He left the town in ruins.
Malphur's mentor, Jaren Ward, confronted Dredgen Yor and was killed by Yor's Thorn.6
Dredgen Yor was finally killed years later by Shin Malphur.7