"Dance, Soterios Johnson, dance, it's a cold world, nobody understands" -Dance, Soterios Johnson, Dance, by Jonathan Coulton
Soterien (so-tee-ree-en) is apparently of Buskan descent, as evidenced by his name. His complete history is unclear. Soterien is very old by Stak's time, but since he's kept young by magic, it does not show in his physical appearance. In his youth, Soterien appears to have been part of some unique order of mages, now long dead.
Soterien has mysterious black metal covering his right arm to the shoulder and his left to the elbow. If he releases his tight control over it, it can extend further up his arms. In his own right, Soterien is not a particularly powerful mage, but these gloves channel power, allowing him to function much like one. The magic they create has an incredibly tight structure and is extremely difficult to deconstruct. In battle, he was Esyrias' equal.
Soterien has no real moral code, but does some feel some loyalty to his allies. He can be cruel or kind, as the fancy strikes him.
Esyrias had few rivals in his time, but Soterien was one of them. The exact relationship between them is now unknown. He seems to feel some affection for Stak, most likely due to his resemblance to Esyrias. At any rate, he hasn't killed him yet.