Borusa was the leader of the True Lords.
Borusa held the title of Magistrix of the True Lords of Gallifrey, a title that Leela thought was equivalent to Imperiatrix. She was curious about Leela, Narvin and Romana, and wanted to check that they weren't vampires. Borusa led one final attack on the vampires before she died soon before Romana opened the transduction barrier. (AUDIO: Annihilation)