Mary Katherine Gallagher is a fictional character invented and portrayed by Saturday Night Live cast member Molly Shannon from 1995 to 2001. She was considered the first breakout character from the new 1995 cast and a significant marker of the increased influence of women writers on the show in the 1990s. Shannon portrayed the character in a 1999 film, Superstar, and she also reprised the role when she hosted Saturday Night Live in 2007. Shannon first created an early version of the character when she was in school at NYU, during a comedy show directed by Madeleine Olnek.

Molly Helen Shannon is an American actress and comedian. Shannon was a cast member on the NBC sketch comedy series Saturday Night Live from 1995 to 2001. In February 2017, she won the Film Independent Spirit Award for Best Supporting Actress for her role in the film Other People.