Yuuzhan Vong from Star Wars would work, their philosophy and religion at any rate. Their whole social structure is redicated on the fact that the only universal truth is pain, we are born in pain, we live through pain and suffering, and we die in pain. Pain is a gift of the Gods and only heretics would shy away from pain. After death the worthy are taken to the Slayer God and stand by his side. To show their devotion to the gods, the vong practice ritual self-mutilation and scarification, with scars showing a kind of rank structure. The most scarred are the most devoted and exalted and lead the war effort. They take pleasure in pain and almost totall subsume the self for the greater good of the Vong and the gods.
They feel that the gods have told them that the galaxy (or in your case the world) belongs to them and they are intent on defeating the infidel and sacrificing those who survive the fighting to their gods.
Match the philosphy and social structure up with any species like orcs or goblins and there you have your fearless foes.