Changer

Changer by Lindskold, Jane. mass_market edition. ISBN: 0071001005998.

Wild, strange, and unpredictable, he is known as the Changer: the ultimate vagabond who slips in and out of myths and cultures, refusing to be pinned down to any one origin just as he refuses to be lcked into any one shape--or name. Yet when a quest for vengeance forces him to shed animal form and seek out King Arthur, the Changer discovers that the darkest of dangers threaten the timeless realm. For Arthurs sworn enemies have risen once more to topple the king and spread chaos among humankind. The Changer himself will be the enemys unwitting accomplice, unless he somehow stops the dreaded forces and diabolical powers threatening to destroy Arthurs kingdom--and all humanity.