Throughout the course of The Simpsons many characters from other movies, TV shows, video games, and cereal brands have appeared.
Characters From Cereal Brands
Captain Quisp appeared in The Way We Weren't when Homer is imagining a perfect world after getting his first kiss from Marge. He eats all the quisp in his spaceship and then eats him.
The Kool-Aid Man
The Kool-Aid Man also appears in Thirty Minutes Over Tokyo. His picture is on the front top of the restaurant America Town.
Characters From Other Comic Books
Characters From Other Movies
Chewbacca from Star Wars appeared in The Springfield Files in the FBI alien line-up. He also appeared in the Bi-Mon-Sci-Fi-Con in Mayored to the Mob. Mark Hamill dressed as Luke Skywalker also appears in the same episode.
Characters From Other TV Shows
ALF first appeared in The Springfield Files in the FBI alien line-up along with Gort, Kang or Kodos, Marvin the Martian, and Chewbacca. He also appears in the picture of characters in Behind the Laughter.
Barney Fife from The Andy-Griffith Show appears in Pranksta Rap when Chief Wiggum finds out how terrible of a chief he is. Wiggum then stares at his TV and then Barney Fife starts speaking to Chief Wiggum saying that he can find the kidnapper and after the conversation Wiggum wonders if that was really Barney Fife or just the actor. He was voiced by Dana Gould.
Barney the Dinosaur
Barney the Dinosaur first appeared in Rosebud when Homer is watching it and Barney is repeating and Homer replies "no wonder why this show is so popular". He makes his second appearance in The Joy of Sect brainwashing Maggie, Baby Gerald, and a bunch of other unnamed babies into loving The Leader. In both appearances he was voiced by Dan Castellaneta.
Bender from Matt Groening's other show Futurama has made three appearances in The Simpsons. He first appeared in the end of Missionary: Impossible as a phone operator, and then in Bart vs. Lisa vs. the Third Grade Bart imagined Richard being Bender. Bender's most current appearance was in Future-Drama in which he comes out of a quantum tunnel which Homer and Bart come out of and says "all right you guys are my new best friends" and Homer replies with "you wish loser" and throws him out of the hover craft. He was voiced by his voice in the series John DiMaggio.
Big Bird from Sesame Street appeared in the episode Missionary: Impossible in which Homer is running away from the various PBS executives and then Big Bird blocks Homer's path.
Elmo from Sesame Street first appeared in Missionary: Impossible in which Homer contributes to PBS and does not have enough money and is chased by an angry mob of PBS characters and then hides in church and Elmo and Oscar the Grouch appear and Elmo says "Elmo knows where you live". He also appears in Bart-Mangled Banner in prison with Bill Clinton, The Dixie Chicks, and Michael Moore saying "Elmo go to wrong fundraiser". He is also mentioned by Ralph in E. Pluribus Wiggum when a republican asks him "who do you like" Ralph replies with "Elmo". He was voiced by Nancy Cartwright.
Kermit the Frog
Kermit the Frog from the Muppets first appeared in Bart the Fink. He was the puppet held by the caricature of John Swartzelder during Krusty's funeral. He later appeared in Troy McClure's Muppet movie in A Fish Called Selma.
Marvin the Martian
Number 6 from the short lived series The Prisoner appears in The Computer Wore Menace Shoes when Homer is relocated to a secret island after knowning too much. He is on the island because he invented an endless bag of chips and for the last 33 years he has been trying to escape using a boat made out of toilet paper rolls, toothpicks, plastic forks, scabs, and dynamite. This is supposed to be a joke that by 2000 the year the episode first aired The Prisoner was cancelled for 33 years. He was voiced by his voice in the series Patrick McGoohan.
Wile E. Coyote
The VeggieTales characters Bob the Tomato and Larry the Cucumber first appear in HOMЯ where they were seen in a booth. They appear again with a carrot in The Greatest Story Ever D'ohed where they tell Homer that he is the new messiah.
Charcters From Other Video Games
Luigi only appeared in the episode Marge Be Not Proud as one of the four video game characters to tell Bart to steal Bonestorm. He was voiced by Hank Azaria who voices the character in The Simpsons named Luigi.
Mario first appeared in the episode Marge Be Not Proud as one of the video game characters who convinced Bart to steal Bonestorm. He makes his second appearance ten years later in Homer and Ned's Hail Mary Pass coming off a bus of Italian people and then taking a picture of him with Homer and then Homer throws barrels at him just like Donkey Kong and then Mario takes goes to Bart's Treehouse and gets a hammer and destroys the barrles and is soon killed by one of them. He was voiced by Dan Castellaneta.
Pac-Man and Ms. Pac-Man
Pac Man appeared in Homer and Ned's Hail Mary Pass when Homer is watching the history of the Super Bowl halftime show and in Super Bowl XVI there was a show with a preacher marrying Pac-Man and Ms. Pac-Man followed by the song Let's Get Physical. Also, Ms. Pac-Man was mentioned in Lisa's First Word when Marge said "Mrs. Pac-Man struck a blow for women's rights". In I Married Marge, Mr. Burns was playing Ms. Pac-Man in his office. A Ms. Pac-Man machine was also seen in Angry Dad: The Movie.
Sonic the Hedgehog
Sonic the Hedgehog first appeared in the episode Marge Be Not Proud as one of the four video game characters to tell Bart to steal Bonestorm. He also appeared in That '90s Show on a billboard with the phrase "marriage comes first" along with Amy Rose. He was voiced by Dan Castellaneta in Marge Be Not Proud and was poorly drawn in that episode as well.
References to Board games
Monopoly appears in Brawl in the Family, where it, among other versions, were choices of games to play during the acid rain. It also appears in Fat Man and Little Boy, in the form of the Duopoly game Bart throws away. In Please Homer, Don't Hammer 'Em, Homer dresses up like Mr. Monopoly. In Thirty Minutes Over Tokyo, Mr. Monopoly is present at a meeting, but drives away in a car resembling the piece in the game when he loses interest.