Faith is the new slayer who was introduced in season 3. Her watcher was killed and she came to Sunnydale to help the famous "B" (her nickname from Buffy) with the slaying. She killed a human by accident in mid third season and has since turned evil. She tried to turn Angel back to being evil (it didn't work) and she and the mayor are working together to destroy everyone. She was killed by Buffy when Angel was dying and needed a slayer's blood to cure him. Her blood wasn't used. Even though she was unconscious, she helped Buffy in her dream to destroy the mayor in the season finale.
Eliza Dushku portrays the now dead Faith. She has also been in movies such as True Lies and others which for some reason I can't remember anymore.
