Cassie — played by Hannah Murray — is an extremely complex character who deals with a host of mental health disorders on the show, like anorexia nervosa, suicidal ideation, and drug addiction. She is also extremely likeable for her eccentricities and gentle nature — but arguably, her most memorable moments in the show are saying "wow" a lot in a breathy voice. After exiting the show with the rest of the cast at the end of season two, Murray had a long stint on Game of Thrones, playing Gilly, and on the 2020 horror series The Expecting.