Almuric

Esau Cairn, a former boxer seeking exile, is transported from Earth to the planet Almuric. Cairn finds human tribes in fortified towns and fights apelike humans, winged demons, and other monsters. By the end of the novel, he and his friends from the towns Khor and Koth must capture Ugg -- citadel of the winged Yaga demons!
A thrilling sword-and-planet novel originally published as a 3-part serial in Weird Tales magazine.