Varda

Varda was located at coordinates vector 3052-Alpha-7-14 span. It was placed in a time loop after the Vardans' failed invasion of Gallifrey. (TV: The Invasion of Time)

Mortimus used Artemis the Chronovore, to release Varda from the time loop and suggested they invade Earth in 1976. This invasion was defeated by the Seventh Doctor, who trapped them in a standing wave that was beamed back to Varda. (PROSE: No Future)