The Wizard
by Gene Wolfe

Description:
A teenager passed from Earth to a magical realm of seven worlds, where he was soon given a hero’s adult body and the name Able. Forced to act as a man, inside he remained a boy, even as he set off to find his destined sword and become a knight. In The Wizard, Sir Able returns to the world of Mythgarthr from Skye following his fight with the dragon Grengarm, twenty years older, with a unicorn steed named Cloud, and special magical powers he has sworn not to use, in return for the hope of meeting his beloved Aelf queen again. He battles the giants, meets gods, heroes, and a sorceress who tries repeatedly to seduce him, and serves the mercurial dragon king Arnthor in a final war with the Osterlings.