My character concept is a man from a tribe of steppe nomads, inspired by such peoples as the Mongols, Turks, Cossacks, etc. You know, horse and bow and all. Spruce it up with a touch of shamanism and tribal magic involving hallucinogens and ritual self-mutilation to channel the power of terrible things (unspecified) that lurk at the precipice between life and death, at the potential cost of the channeler's sanity.

I have an idea for my religious beliefs where it's thought that if a person is murdered, their spirit cannot find rest until they're avenged (some tie-in here with my shamanistic magic is quite possible here, I reckon), and it falls upon kin and tribesmen to carry out vengeance. Debts and especially revenge will be important in my people's culture. 

I want to work this into my character's motivations for fighting Dagon somehow, but I'm not sure yet how I'll connect all of this. I've thought of my tribe having a kind of vassal relationship with the kingdom of Varyon, or maybe they're just rubbing up against Dagon's border enough to warrant his wrath. (These kinds of peoples are famed for being a menace to societies that border them, after all...)