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:
And some single volumes: