Katherine Evelyn Anita Cassidy (born November 25, 1986) is an American actress. Following several minor television roles, she came to attention as a scream queen after starring in the horror films When a Stranger Calls (2006), as Kelli Presley in Black Christmas (2006) and as Ruby in the third season of the horror series Supernatural (2007–2008). Following a supporting role in the action film Taken (2008), Cassidy played leading roles in the mystery horror series Harper's Island (2009) and the remake of the drama series Melrose Place (2009–2010). She starred as Kris Fowles in the slasher film remake A Nightmare on Elm Street (2010) and had a recurring role as Juliet Sharp during the fourth season of the teen drama Gossip Girl (2010–2012). Cassidy had her breakthrough in 2012, after being cast as Laurel Lance / Black Canary, on The CW television series Arrow. Cassidy has reprised her role in the Arrowverse series The Flash and Legends of Tomorrow, as well as voicing the character in the animated web series Vixen. Following her character's death in season four of Arrow, Cassidy began playing Laurel Lance / Black Siren, an antagonistic version of the character from a parallel universe, originating on The Flash and continuing on to Arrow. She is the child from the short-lived relationship of actor and singer David Cassidy and fashion model Sherry Williams.
In October 2008, Variety announced Cassidy had been cast on the CBS horror mystery limited series Harper's Island. Cassidy portrayed the role of Patricia "Trish" Wellington, a bride-to-be. The series centered on a group of family and friends who gather for a wedding on an island known for its sinister past full of gruesome murders. In each episode, at least one character is killed off. Cassidy and her fellow cast members were not told about their characters' deaths until the day they received a script. The series premiered on April 9, 2009 to 10.21 million viewers. Despite ratings failing to maintain the pilot's success, CBS aired the remainder of the series with the series finale airing on July 11, 2009.