Downtiming the Night Side

Notorious but better-than-it-sounds science fiction novel by the equally notorious Jack L. Chalker. It posits a world in which Time Travel to or from the past is possible by "leaping" into the body of a person of that time. There is a catch: spend too much time in the past, and you'll 'trip' and be stuck as that person permanently, even if you return to the present.

When the hero's first leap into the past uncovers a full-fledged war for control of the future, things go from bad to worse very, very quickly.

Predates Quantum Leap by more than a decade.

Tropes:

 * All the Myriad Ways: History is changed several times -- sometimes drastically -- over the course of the story.
 * Author Appeal: It is Chalker, after all.
 * Brother-Sister Incest: Guess what happens when you grow up on a desert island with no one but your parents and siblings for company?
 * Butterfly Effect: Subverted: you have to kill someone really important to significantly affect the outcome of history. If you killed someone in the Middle Ages who was an ancestor of, say, Teddy Roosevelt, there'd still be enough genes in the pool for someone to give birth to Teddy Roosevelt hundreds of years later. History is like a big river and it "flows" around small impediments.
 * Different for Girls: Specifically averted by The Mind Is a Plaything of The Body.
 * The Dragon: Eric Benoni.
 * Even Bad Men Love Their Mamas
 * In Spite of a Nail
 * Mental Time Travel
 * Ret Gone: The goal of the war is to do this to the enemy.
 * Ripple Effect Proof Memory: Mildly subverted: You lose some of yourself (and gain some of the personality of your new host) every time you 'trip'.
 * Disappeared Dad: The driving force behind the Dragon.
 * Place Beyond Time: Not really, but the heroes' base is in the early Cenozoic, far enough back so plate tectonics will destroy all of the evidence.
 * San Dimas Time: The "edge" in the future is always moving.
 * Sci Fi
 * Screw Yourself: And have lots of children doing it.
 * Set Right What Once Went Wrong
 * Self Made Orphan: Combined with Truly Single Parent and Even Bad Men Love Their Mamas in a way that only a Timey-Wimey Ball makes possible.
 * Stable Time Loop: Used to "nightside" people by cutting them off from their prior selves.
 * Temporal Paradox: Several.
 * Time Machine
 * Timey-Wimey Ball: And how.
 * Time Police: The hero is forcibly recruited.
 * Truly Single Parent: Using a Gender Bender and a Stable Time Loop instead of cloning, but still...
 * Unfortunate Names: Ron Moosic, the Hero.
 * The War of Earthly Aggression: The time war proves to be a second front.
 * Word of God: Chalker claimed that he wrote this story in an attempt to address the questions raised--but not answered --by Robert A. Heinlein's "All You Zombies".
 * You Already Changed the Past: Used, averted, and subverted as the hero experiences several time loops from various perspectives.