Ninth Sister was an Inquisitor who served Darth Sidious and Darth Vader in the comic series Darth Vader: Dark Lord of the Sith.
Ninth Sister debuted in Issue 6 – The Chosen One, Part VI. She has so far appeared in eight other issue of Darth Vader including five issues of the Burning Seas arc.
Check out the entire list of women in 365 Days of Star Wars Women in the Women in Star Wars Index. It includes highlights from each post plus notes which posts include new 365 interviews with actresses, writers, artists, and more.