Doom found Jarred after he had lost the Grey Guards following him from Dread Mountain. He tended to Jarred's wounds and brought the injured man back to health. However, the Grey Guards found the trail again and came to Kinrest, looking for Jarred. Doom faced them alone, and was overwhelmed. He was then avenged by Jarred, who slew the remaining Grey Guards.
After his death, Jarred buried him, and erected a tombstone, swearing revenge. Then he took the name of Doom, since he had forgotten his own.
Lief, Barda, and Jasmine rest in Kinrest on their way to Dread Mountain. While there, they discover Doom's gravestone, which leads them to wonder about the man who now uses his name.
The Valley of the Lost
After being forced to walk into Tora to prove he was not an Ol, Jarred, still without his memories, tells the companions about his meeting with Doom, and why he took his name.
Doom was skilled in the healing arts, as he was able to save Jarred, who was on the verge of death. He was not a fighter, and as such, had no chance against the Grey Guards who attacked him.
In the anime, he was actually described to be a skilled warrior but ultimately no match for an entire pod of Grey Guards.
Jarred called Doom 'a man of peace' who had 'no chance against' the Grey Guards who attacked him.
Doom's name could foreshadow his ill fate, for which he was 'doomed' to die.