Mary Kay Bergman (June 5, 1961 – November 11, 1999), also credited as Shannen Cassidy, was an American voice actress and voice-over teacher. Bergman was the lead female voice actress on South Park from the show's 1997 debut until her death. Throughout her career, Bergman performed voice work for over 400 television commercials and voiced over 100 cartoon, film, and video game characters.

Born in Los Angeles, Bergman had an interest in fantasy and animation early in her life. She acted in plays during high school and also studied theater at University of California, Los Angeles (UCLA). After struggling to secure on-screen acting jobs, she began taking work as a voice-over actress. In 1989, she began voicing the Disney character Snow White. In the 1990s, she voiced Daphne Blake in three films from the Scooby Doo franchise as well as Timmy Turner in the Oh Yeah! Cartoons.

Shortly after her death, her husband Dino Andrade established the Mary Kay Bergman Memorial Fund.