Not much is ever revealed about Soren's past. What is known is that he is almost as old as Viktor himself and that he has a surprising lack of personal ambition, and, being two of a kind, he has a great rivalry with Raze.
Soren served as the head torturer in Viktor's employ. He proved to be very skilled in taming Lycan slaves with silver edged whips, and even used them on Lucian at Viktor's request prior to Sonja's execution.
At some point (presumably while Viktor was hibernating), Soren attached himself to the regent of Viktor's estate, Kraven. After serving as Kraven's bodyguard for many years, he became the leader of Kraven's "secret police", a group of thugs loyal to Kraven which he created opposite to Viktor's Death Dealers.
Soren also acted as Kraven's chauffeur, and often accompanied him when the latter was meeting with Lucian, who had Raze accompany him. It was because of Soren's previous torture of Lucian (whom Raze deeply honored) that Soren and Raze acquired a deep personal hatred and rivalry. In a final battle during the Death Dealers' raid on the Lycans' compound, Soren was eventually killed by Raze despite his use of his silver-studded whips.