Dame Judith Underdunk (Tress MacNeille) is a hidden villainess from "Funeral for a Fiend," episode 19.08 of The Simpsons (airdate November 25, 2007). She is a legendary Shakespearean actress, as well as wife of Dr. Robert Terwilliger, Sr. She is also the mother of Sideshow Bob and Cecil Terwilliger, the mother-in-law of Bob's wife, Francesca, and the grandmother of Bob and Francesca's son, Gino.
Judith was shown during Bob's trial for his latest attempt to kill the Simpsons, and was badgered with questions from devoted fan Lenny Leonard. The trial saw Bob claim that his murderous intentions were the result of being harassed by Bart, and ended with Bob suddenly dropping dead, with Judith stating that Bob had a heart ailment.
It was revealed in the episode's climax that Bob (with his father's help) faked his death, and Judith was a villainous conspirator in her son's latest plan to kill Bart. Judith's reveal came when she and Robert removed their police disguises after bringing Cecil to the funeral home (where Bart's attempted murder was to take place), and following the reveal, Judith cackled evilly along with the rest of the family, who were in on the scheme. Their plan was later thwarted by Lisa, who pointed out that Bob's casket provided extra room for his large feet, as it was odd that his family would pay for the comfort of a dead man. Judith was arrested, along with the rest of the Terwilliger family.
- An assumption could be made that Dame Judith Underdunk was created as a caricature of famed actress Dame Judi Dench.
- The revealed name of Sideshow Bob's mother also reveals where his middle name, Underdunk, came from. Her appearance also reveals that Bob and Cecil inherited their mother's hairstyle, and it was passed down to Bob's son, Gino.
- Tress MacNeille voiced another Matt Groening villainess when she recurred as Mom on Futurama. She also voiced villainesses Mary Beth on Freakazoid!, Colleen on Road Rovers, Hama from Avatar: The Last Airbender, and the Jeweler's Wife from Timon & Pumbaa.