OP if you liked these since no one else mentioned it, might I suggest you check out Micheal Moorcock? He was one of the first SF authors to do a multiverse and his influence on SF and fantasy is vast. His main work is a series of characters tangentially connected all together call "The Eternal Champion". There are many different champions but the most famous you might dig - Elric of Melnebone.

You will be surprised to realize his work started on the character back in 1961 and see how many tropes come from his efforts.