Time Patrol

Time Patrol is a series of works, mostly short stories, by Poul Anderson. They take place in a universe where the resolution to the Grandfather Paradox is that you now exist without ever have had a father, and the Time Police relentlessly works to keep time nevertheless on the same path -- while ruthlessly expurgating futures, filled with living beings, that do not conform to it. Doing this often requires the sacrifice of time travelers or those they love.

Tropes featured

 * Ancient Astronauts: Except with time travelers.
 * The Atoner: Harpagus in "Brave To Be A King"
 * Bittersweet Ending: Typically.
 * Briar Patching: Manse warns the Mongols that the distilled liquors are too strong for them.
 * The Chosen One: Invoked in "Brave To Be A King" to restore history
 * Dreaming of Things to Come: In "Brave To Be King" used to explain an infanticide
 * Light Is Good: Invoked in the Persian setting of "Brave To Be A King"
 * Moses in The Bulrushes: in "Brave To Be A King" twisted
 * Ontological Inertia: Temporal inertia makes it hard to change the past -- including changing it back.
 * Time Machine: The members of the Patrol use vehicles ranging from one- or two-person motorcycle-like "time scooters" to larger, multi-passenger time transports.
 * Time Travel
 * Time Travel Tense Trouble: Averted by inventing a language, Temporal, with more tenses.
 * Timey-Wimey Ball: All the changes. . ..
 * Tricked Out Time: Features such wonders and abuse of the self-consistency principle that when a man sees his lover falling off a cliff, he turns his head, so that he doesn't see her hit bottom and can come back and rescue her later.
 * Will Not Tell a Lie: Persians in "Brave To Be A King"
 * You Will Be Beethoven: Or Cyrus the Great. Or Odin.