Robert Underdunk Terwilliger Jr., PhD, better known as Sideshow Bob, is a recurring character in the animated television series The Simpsons. He is voiced by Kelsey Grammer and first appeared in the episode "The Telltale Head". Bob is a self-proclaimed genius who is a graduate of Yale University and a champion of high culture, including the adoption of a transatlantic accent, similar to that of Grammer's portrayal of Dr. Frasier Crane from the sitcoms Cheers and Frasier. He began his career as a sidekick on Krusty the Clown's television show, but after enduring constant abuse, Bob framed his employer for armed robbery in "Krusty Gets Busted", only to be foiled by Bart Simpson, and sent to prison. Bob started seeking revenge against Bart while in prison, and the two became feuding arch-enemies.

Bartholomew Jojo "Bart" Simpson is a fictional character in the American animated television series The Simpsons and part of the Simpson family. He is voiced by Nancy Cartwright and first appeared on television in The Tracey Ullman Show short "Good Night" on April 19, 1987. Cartoonist Matt Groening created and designed Bart while waiting in the lobby of James L. Brooks' office. Groening had been called to pitch a series of shorts based on his comic strip, Life in Hell, but instead decided to create a new set of characters. While the rest of the characters were named after Groening's family members, Bart's name is an anagram of the word brat. After appearing on The Tracey Ullman Show for two years, the Simpson family received its own series on Fox, which debuted December 17, 1989. Bart has appeared in every Simpsons episode except "Four Great Women and a Manicure".