The "Bad Wolf entity" is a fictional concept from the British television series Doctor Who. It represents a mysterious force that influences events and characters throughout the show's storyline, particularly in the episodes featuring the Ninth Doctor, played by Christopher Eccleston, and the Tenth Doctor, played by David Tennant. In the series, the Bad Wolf entity is linked to the character Rose Tyler, portrayed by Billie Piper. It symbolizes the idea of a powerful, omnipresent force that can manipulate time and space, ultimately leading to significant changes in the narrative and the characters' fates.