Nobody knows what possessed Rashak's mother to fall in love with an orc, but actually as far as anyone can tell, theirs was a happy marriage. She was a Mwangi mystic, an oracle of the heavens who was drawn to the Worldwound presumably by the same calling that attracted her to Shorok, Rashak's father.
Shorok was, for his matter, a rather unusual orc, kind of a paragon of virtue for his race. Sure, he was prone to bashing things when he did not get his will and he never claimed to be unselfish or forgiving, but he managed to transform his craving for violence into something useful as he joined the Crusade as a Low Templar. That's where he met Lorna, Rashak's mother, who recruited him as a Riftwarden.
Their untimely disappearance right after young Rashak was born has only added to the myths of the mismatched couple. They have been missing for twenty years now, failing to return from their very first mission, leaving young Rashak to fend for himself in a hostile world.
Initially his father's clan claimed him, which almost killed him, as the rough life of a mercenary camp is no place for a child, but eventually he was rescued. In his own mind it was the mystic power of his birthmark that kept him alive. Maybe because of his horrible experiences, maybe because he shared his mother's calling that had manifested in a strange birtmark, he turned quite bookish and reclusive, and spent most of his time in libraries and doing apprentice work for various wizards.
For a half-orc he is surprisingly docile and kind, but he prefers not to let anyone know what he is thinking.