Ruby.

About Ruby

Ruby is a demon on The CW's Supernatural, portrayed mainly by actresses Katie Cassidy and Genevieve Cortese. Created by the writers to expand on the characterization of demons within the series, she first appears in the third season, wherein she assists series protagonists Sam and Dean Winchester in fighting her fellow demons. By the fourth season, she has won Sam's trust and begins training him to kill demons with his psychic powers, though Dean remains fearful of ulterior motives. The character is killed at the end of the fourth season. In the fifteenth season, Ruby returns through flashbacks and a visit to the Empty, the angels' and demons' afterlife.