Rough backstory idea (if you'd prefer a more standard way to learning my class abilities I can change it):
Hrothgar's tribe had been striving to make a living on Itanat for as long as anyone could remember, but unfortunately that didn't mean much. As he grew, it became clear that Hrothgar was stronger and hardier than his peers and seemed more adapted to living in the harsh environment. The fog had just as much of an affect on him as the other orcs, but Hrothgar recovered from it quickly as long as he wasn't away from it for too long.
Unfortunately for the rest of the tribe, Hrothgar's differences were more than they realized. It was as if he had been infused with the nature of the plane. He practiced in secret, learning how to channel the powers of death through his attacks. He also learned that he could heal, although even his healing was a bit necromantic as he had to strike a foe and channel that life force into a friend.
When his abilities were discovered, Hrothgar was confronted by his friend Gork. After a brief scuffle Gork was dead although Hrothgar had only touched him. Knowing that he had to do something, Hrothgar used all of his concentration trying to bring his friend back. And he did, as an undead creature. With all of the witnesses Hrothgar had no choice but to flee with Gork in tow.
They wandered together through the fog, keeping to the safest areas until Hrothgar found Necra and became fascinated. Here was a being fueled by death even more than Hrothgar was! With Necra and Gork as his best friends, no one could stop them!