Question: On which television show does Katie Cassidy play the fictional character, Ruby?
Sentence (from "Supernatural (season 3)"): They become allies with a demon named Ruby (Katie Cassidy), who claims to know a way to release Dean from his demonic pact—he had sold his soul to a demon and was given a year to live in exchange for Sam's resurrection—and wants to protect them from the new demonic leader Lilith.
Relevant evidence: No