Epemitreus

Epemitreus the Sage is a character who appears in the The Phoenix on the Sword story by Robert E. Howard. He appears to Conan in a dream to warn him of danger and darkness looming around him, and tells him of how he spent his life fighting the forces of the god Set and his followers. Epemitreus  magically carves a symbol into the cross-guard of Conan's sword. Conan wakes up in his chamber, sword in hand, and is bewildered by the fact that his sword now has a phoenix carved into the cross-guard, just like in the dream.

Epemitreus led the Hyborians' fight against and crushing of Acheron, and was the founder of the cult of Mitra. He might also be the shaman who used the heart of Ahriman against Xaltotun of Python.

Trivia
Epemitreus sitting sleeping in a cave (Mount Golamira) and allegedly having lived three ordinary lifetimes resemble legends about Epimenides, a historical religious reformer in ancient Greece: A worshipper of Apollo, whose land was Hyperborea. Epimenides is said to have slept for decades in the cave on Crete where Zeus is said to have been born.