The Eternal Champion — Michael Moorcock

From one of Britain's foremost fantasy writers comes this Tolkienesque series opener about destiny, war, betrayal -- and the return of a long-dead hero
 
John Daker dreams of other worlds, and a name: Erekosë. He finds the strength to answer the call, travelling to a strange land ruled by the aging King Rigenos of Necranal.
 
Humanity is united in a desperate fight against the inhuman Eldren, and John must fight with them. But the actions of his brethren turn his loyalties -- and, as Erekosë, he will take a terrible revenge.