A very prolific science fiction/fantasy/sf author. His common themes are transformations of all types (but most commonly gender changes and changes to alien/fantasy races) alternate universes (especially fantasy and either high-tech or maybe just normal, present-day Earth-like worlds that somehow cross or exchange characters), reinterpretation of religious beliefs, and the great machine that runs everything.

Some series by Jack Chalker:

• the Well of Souls (8 vol.)
• the Rings of the Master (4)
• the Dancing Gods (5)
• the Wonderland Gambit (3)
• the Quintara Marathon (3)
• the Changewinds (3)
• the Four Lords of the Diamond (4)
• Soul Rider (5)

And some single volumes:

• The Identity Matrix
• Downtiming the Night Side