Question: On which television show does Katie Cassidy play the fictional character, Ruby?
Context: Ruby Buckton is a fictional character from the Australian Channel Seven soap opera "Home and Away", played by Rebecca Breeds.  She debuted on-screen during the episode airing on 20 June 2008.  Ruby was created by executive producer Cameron Welsh.  When she was first introduced she appeared to hide her problems and pretends to be strong.  She was characterised as a free spirited and independent girl.  Her storylines have consistently followed themes such as romance, unrequited love and rejection.  In what has been described as a "shock storyline" Ruby discovered her sister Charlie Buckton was in fact her mother.  This had subsequent effects in her character development.  She became out of place and confused about her life.  It destroyed her trust in Charlie and their relationship never recovered.  Ruby went on a journey of self-discovery and used men to redefine herself.  Her relationship with Xavier Austin was characterised through their mutual friendship, which ended through lack of passion.  She controversially fell in love with her music teacher Liam Murphy, the pair shared an emotional and creative connection through music.  Yet, her advances were unrequited and it created problems with her state of mind and began binge drinking.  Breeds felt the storyline differed to her romance with Xavier, as it showed Ruby "headstrong and unconfined".  Breeds felt they were ill-suited to one another. The third season of "Supernatural", an American fantasy horror television series created by Eric Kripke, premiered on October 4, 2007, and concluded on May 15, 2008.  Traveling throughout America, protagonists Sam (Jared Padalecki) and Dean Winchester (Jensen Ackles) use their father's journal to help them carry on the family business—saving people and hunting supernatural creatures.  The season begins with the brothers tracking down the demons released from Hell in the previous season finale.  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.  As Dean's deadline approaches, their efforts are further hindered by Bela Talbot (Lauren Cohan), a professional thief of occult items who is often at odds with the Winchesters. Katherine Evelyn Anita Cassidy (born November 25, 1986) is an American actress.  After initially appearing in minor television roles, she made her film debut in "When a Stranger Calls" (2006).  During the same year, she also had her first starring role as Kelli Presley in "Black Christmas" (2006).  In 2007, Cassidy gained attention for her role as Ruby on the supernatural-horror television series "Supernatural", during its third season.  She later had a supporting role in "Taken".  In 2009, Cassidy became a cast member of the series "Harper's Island" and "Melrose Place", both of which lasted for only one season.  During 2010, she had a supporting role as Kris Fowles in "A Nightmare on Elm Street" and a recurring role during the fourth season of "Gossip Girl". The pilot episode of the television series "Arrow" premiered on The CW on October 10, 2012.  It was written by series developers Greg Berlanti, Marc Guggenheim and Andrew Kreisberg, and directed by David Nutter.  The episode introduces Oliver Queen (Stephen Amell), a billionaire playboy, his mother Moira Queen (Susanna Thompson), sister Thea (Willa Holland), new bodyguard John Diggle (David Ramsey), best friend Tommy Merlyn (Colin Donnell), ex-girlfriend Laurel Lance (Katie Cassidy), and her father Detective Quentin Lance (Paul Blackthorne).  It follows Oliver as he returns to Starling City, after having been shipwrecked for five years, and becomes a bow-wielding, hooded vigilante who sets out to right the wrongs of his father, who died during the shipwreck, and save the city. Juliet Sharp is a recurring character who exclusively appeared in the "Gossip Girl" television adaptation.  The character was created by "Gossip Girl" producer Stephanie Savage and is portrayed by actress Katie Cassidy.  The series portrays her as a scheming and secretive but caring woman who develops into a formidable antagonist as her agenda against Serena van der Woodsen progressed.  The actions of character has drawn comparisons to another villain of "Gossip Girl", Georgina Sparks, and received positive reviews for her inclusion in the series.  Juliet only appears during the first half of the fourth season, though she returns in the series finale. Ruby is a fictional character on The CW Television Network'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 departs the series at the end of the fourth season.  Though the fans at first reacted negatively towards Cortese replacing Cassidy after the third season, Cortese and creator Eric Kripke felt that they became more accepting as the fourth season progressed.  While fan response to the character was mixed overall, critical reception was generally negative.  A common criticism was underwhelming performances by Cassidy and Cortese. Kelli Presley is a fictional character in the "Black Christmas" franchise.  The character, created by writer-director Glen Morgan and portrayed by actress Katie Cassidy, serves as the primary protagonist and final girl of the "Black Christmas" remake, acting as a replacement to Jess from the original film. Detective Brian Cassidy is a fictional character played by Dean Winters in the American crime drama television series "" on NBC.  A recurring cast member during the first season, Cassidy is a young and inexperienced detective with the New York Police Department's Special Victims Unit, and the original partner of John Munch (Richard Belzer).  The stress of the Special Victims Unit is too much for Cassidy, and he transfers to the Narcotics unit in the middle of the season.  Cassidy later returns in the finale working undercover for a pimp the SVU detectives are investigating. Christina "Tina" Gray (named Christina "Kris" Fowles in the 2010 reboot) is a fictional character in the "A Nightmare on Elm Street" franchise.  She was created by Wes Craven.  The character was portrayed by Amanda Wyss in the original film and Katie Cassidy in the 2010 film.  A high school student whose death is the catalyst for the events of the series, Gray is the false protagonist of the 1984 original film.  She also appears in the novels, "Wes Craven's New Nightmare" (1994), "Freddy vs. Jason" (2003), 2010 reboot, merchandise based on the films, and a claymation version of the character is shown in the documentary "" (2010).  The imagery featuring Gray in the body bag during the dream sequences have been regarded as iconic. Rose Nylund (née Lindström) is a fictional character featured on the popular 1980s situation comedy "The Golden Girls", and its spin-off "The Golden Palace".  She was portrayed by Betty White for 8 years, totaling 208 episodes.  Rose was originally supposed to be played by Rue McClanahan, whereas Blanche Devereaux, one of Rose's roommates, was to be played by White.  However, Jay Sandrich, the director of the show, suggested that Betty and Rue switch parts.  He felt that Betty would be a better fit for Rose because she had already played Sue Ann Nivens in the television show "The Mary Tyler Moore Show", which is similar to the character of Blanche Devereaux.  In a January 2017 interview with Katie Couric, White stated she jumped at the opportunity to take the role of Rose, noting she loved the character and describing Rose as "so innocent, not the brightest nickel in the drawer, but funny."
Answer: Supernatural