The Godfighter championed the mortals against what he saw as oppression and abuse by immortal beings. The legends say the gods feared him but he did fall in time.
My research shows that the gods he fought were the gods of Stormheim. Odyn, in particular. The Godfighter's shield took so much damage from lightning bolts that it became lightningsteel. After the Godfighter died, Odyn took the shield and melted it down as a trophy. Get that lightningsteel from him and forge a hammer from it.