Nine Princes in Amber by Roger Zelazny
The first book in the Amber series. Two sets of five books, plus a fist full of short stories and an amazing amount of fan fiction. It starts with a common theme for the author. The protagonist has to discover who he is, and why he is in a bunch of trouble. In this case he just isn’t a very long lived mercenary who wakes up in a private ‘sanatorium’, where the staff tries to keep him heavily sedated. Nope, nothing that simple. It gets weirder from there damn quick and stays there! Zelazny has the delightful talent of taking the line between fantasy and Science Fiction and using it to play jump rope. For Carl Corey is really Prince Corwin of Amber. The Kingdom at the center of all the varied realities. Toss in some wonderfully detailed sword fights (Zelazny was a fencer and an Aikido instructor), massive battles, treachery, and that special blend of wry Zelazny humor, and you will be be looking for the next book in the series straight off.