Theory on Luc and Isam formation
We never get an answer in the books, and to my knowledge Jordan never provided more detail other than a creation of the dark one. The theory that one of them is a corrupted wolf brother has been floated before, but no confirmation.
We know that:
Darkhounds hate wolves, and forget they were wolves once. When a darkhound eats the soul of a not quite dead wolf, a new darkhound can arise (from Elyas)
In the prophecies of the shadow, we hear:
Luc came to the Mountains of Dhoom. Isam waited in the high passes.
The hunt is now begun.
One did live, and one did die, but both are.
There is at least the possibility they can eat men’s souls:
“Perrin reined in, though he itched to keep moving. Shadowbrothers. The wolves’ name for Darkhounds had taken on a new grimness. “Can they eat a man’s soul, Elyas? Say a man who can talk to wolves?” Elyas shrugged. Only a handful of people could do what they did, as far as either man knew. An answer to that question might come only at the point of death. More importantly right then, if they had been wolves, once, they must be intelligent enough to report what they found.”
What if the hunt is now begun also refers to the Darkhounds? And they killed luc and isam, with one or both being wolf brothers corrupted by Darkhounds, with their souls combined into a new darkman?