The Chronicles of Amber
"The Chronicles of Amber" is a fantasy series written by Roger Zelazny chiefly in ten books published from 1970 to 1991. It features a great variety of characters from a myriad parallel universes (including "our" Earth universe). All universes spiral out on a continuum, which are more closely related to one end, Amber (and its history and functions), or slides on a scale closer and closer to Amber's opposite, the Courts of Chaos, at the other.