These are characters from the animated TV series The Simpsons.
Spoiler warning: Plot or ending details follow.
Characters are only listed once, normally under the first applicable subsection in the list; very minor characters are listed with a more regular character they are associated with. Subsections are ordered by size and ongoing relevance to the show.
Tibor, general company scape-goat due to his inability to speak English, promoted ahead of Homer.
Gummy Joe
Stewart, a duck hired as a cheap courier
Jack Marley (retired)
Mindy Simmons (fired), formed a close friendship with Homer which tempted him almost to adultery.
Frank Grimes, a.k.a. Grimey (deceased), killed self while angrily denouncing Homer
Karl, former executive assistant of Homer, (dismissed) (voiced by Harvey Fierstein)
Pops Freshenmeyer
Blinky, three-eyed fish, sometime mascot, one of many so mutated due to power plant's radiation
An entire Braziliansoccer team has been noted as working in the reactor core. (When the nuclear regulatory commission criticised Mr. Burns on this, he replied "That plane crash landed on my property!" )
Related:
Aristotle Amadopolis, owner, Shelbyville Nuclear Power Plant
SideShow Bob, tried to kill Bart Simpson and Krusty the Clown
Business Figures
Lionel Hutz, incompetent lawyer and one time real estate broker
Unnamed, corporate attorney, nasally and pasty-faced lawyer with blue hair. Differs from Hutz in that he is actually competent
Gil, incompetent lawyer, as well as incompetent salesman of real estate, cars, shoes, computers (a parody of Jack Lemmon's character in the movie Glengarry Glen Ross)
Colonel Antoine "Tex" O'Hara, oil tycoon, former owner Springfield Isotopes, former owner She's The Fastest greyhound, owner traveling carnival, humidor maker
Howard K. Duff VIII, owner Duff Beer, owner Springfield Isotopes
Barry "Duff Man" Duffman, product promoter (current holder of the title, others were Larry & Sid)
Jack Larson, president Laramie Cigarettes
Lindsey Naegle, entrepreneur, alcoholic, sexual predator
Cookie Kwan, successful Korean-American realtor (Cookie's "number one on the West Side")
Jeff Albertson, a.k.a. Comic Book Guy, owner Android's Dungeon Comics & Baseball Card Shop. Characters call him "Comic Book Guy", his actual name was revealed in the 2005 episode #1602 "Homer and Ned's Hail Mary Pass". Prior to this episode, Matt Groening suggested his name was "Louis Lane", but this name was never used in a Simpsons episode.
Unnamed "Yes" guy, restauranteur, waiter and host (a Frank Nelson parody). He explains his condition by saying that he had a stroke. Sound Clip (ftp://ftp.smoovenet.com/pub/lardlad/sounds/season10/mayor22.mp3)
Akira, restauranteur behind the Happy Sumo; and part-time martial-art teacher (Voiced by George Takei)
John, gay antiques owner of store in Springfield Mall (voiced by John Waters)
Captain Horratio McAllister (The Sea Captain), restauranteur behind the Frying Dutchman and charter boat operator. In court, it was proven that he is not actually a real captain, although he has been seen piloting various vessels over the course of the series. He was responsible for helping young Homer cross a lake at his summer camp to meet Marge for the first time. In several episodes he has been shown to have a prosthetic leg, a glass eye, a problem with alcohol, to be bisexual, and to suffer from crippling depression. His catch phrase is a piratical "Yaaaarr".
Squeaky-voiced teen, nameless, fills various positions at entry-level part-time jobs around Springfield
'Mom', tough girl at Mom and Pop's hardware store, onetime girlfriend of squeaky-voiced teen (who was 'Pop' in the same store)
Herman, one-armed veteran, owner Herman's Military Antiques and a smuggler of cheaply-made pants
Professor John Frink, scientist, inventor, entrepreneur, and ex-lecturer at the University of Springfield (based on Jerry Lewis' character in The Nutty Professor)
Goose Gladwell, eccentric Willy Wonkaesque clothing and novelty store entrepreneur who screws Bart on a business deal
Unnamed "Klav Khalash" guy, sells meat on a stick and crab juice to Homer in New York City, and is seen in the Russian district of Springfield when Lisa gets the bus.
Local Media Personalities
Television
Krusty the Klown, Herschel Schmoikel Pinkus Krustovsky, entertainer
Rabbi Hyman Krustovsky, rabbi and Krusty's formerly estranged father
Sophie, Krusty's daughter
Lois Pennycandy, Krusty's personal assistant
Sideshow Bob, Robert Underdunk Terwilliger, former sidekick of Krusty, repeat attempted-murderer, fraudulently elected major of Springfield for a short time
Cecil Terwilleger, Bob's jealous younger brother
Sideshow Mel, Melvin Van Horn, Bob's humble but eloquent replacement
Sideshow Raheem, angry, angry young man
Mr. Teeny, trained monkey on Krusty's show, uncle was former minister of tourism of Brazil; there have been three Mr. Teenys that died who have been used by Krusty
Corporal Punishment, background player on Krusty's show
Tina Ballerina, another Krusty regular
Ms. No Means No, mandatory Krusty add-on after a sexual harassment suit
Kent Brockman, local anchorman for KBBL-TV (Channel 6), real name Kenny Brockelstein
Arnie Pye, "Arnie in the Sky," disgruntled Channel 6 traffic helicopter reporter
Bumblebee Man, Mexican language television host on KMEX-TV (Channel Ocho), real name likely Pedro
Emma, Bumblebee Man's ex-wife
Unnamed actor, the hard-nosed television character MacGarnicle in the show of the same name
Lurleen Lumpkin, country western singer/songwriter, currently in rehab
Be Sharps, Grammy winning barbershop quartet (consisting of Homer, Apu, Skinner and Barney - and Chief Wiggum who left/got thrown out before they became famous)
Party Posse, boyband (consisting of Bart, Milhouse, Nelson and Ralph)
Rachel Jordan/Kovenant, Christian rock
Larry Davis Band, frequent live performers at local functions
Sports & Other Personalities
Anton Lubchenko, football player for Springfield University
Drederick Tatum, professional heavy-weight boxer (and convicted felon). Parody of boxer Mike Tyson.
Lucius Sweet, professional boxing promoter (parody of boxing manager / promoter, Don King)
Rasputin the Friendly Russian, formerly the Mad Russian, professional wrestler
Dr. Hillbilly, professional wrestler
Iron Yuppie, professional wrestler
Professor Werner von Brawn, professional wrestler
Clay Babcock, two-time Fast Car champion
Ronnie Beck, three-time soapbox derby champion
Stan "The Boy" Taylor, football player, Springfield Atoms
Flash Bailey, baseball player, Springfield Isotopes
Captain Lance Murdock, daredevil
Box Car Fred (and various other hobos), boxing runner-ups
Disco Stu, 70s disco king who always wears lesuire suits
Scorpio, supervillain and very considerate and friendly employer
Bowling teams:
Pin Pals (consisting of Homer, Apu, Moe, and Otto, before he was replaced by Mr. Burns)
The Holy Rollers (consisting of Ned, Maude and the Lovejoys)
The Stereotypes (consisting of Willy, Capt. McAllister, Luigi and Cletus)
The Homewreckers (consisting of Jacques, Princess Kashmir, and two unknown women)
DMV Regulation Kings (consisting of Patty, Selma, and two other DMV employees)
Channel 6 Wastelanders (consisting of Kent Brockman, Arnie Pie, Krusty and Bumblebee man)
Springfield Police Framers (consisting of Wiggum, Lou, Eddie and Snake) (disbanded)