Ailla (The Dark Path)

Ailla was the Master's Companion and lover when he was still Koschei. She was a Time Lady, and an undercover agent of the Celestial Intervention Agency to spy on the Master.

When Ailla appears alive, after Koschei has destroyed an entire planet to try to bring her back, it proves to be too much for him. Her betrayal and his murder of a planet is believed to have been the catalyst for turning Koschei into the Master that seeks to control the universe.