Being a Long Runner, The Simpsons has featured a lot of memorable characters over the years.
- Apu is a good example of recurring Ensemble Darkhorse. First he started out as the typical Indian cashier, with his only acknowledged relative being his brother Sanjay, and then he got a few episodes centered around him. For Character Development, he even got a wife and eight children. He might also act as the Simpsons' Sixth Ranger, as seen in The Simpsons Hit & Run.
- Milhouse, even before his memehood was disputed.
- Ralph Wiggum is a great example of Flanderization that was praised by the fans. He became this after he transformed from an average kid to the show's village idiot.
- Sideshow Bob. Originally he was going to be a one-shot villain, but has kept coming back. He has been voted the 66th greatest villain of all time. It helps that Kelsey Grammer is his voice actor. The writers even wanted him to be included one episode every season, but even they could not come up with reasons for him to show up all the time.
- A popular one-time character is Linguo, Lisa's Grammar Nazi robot from "Trilogy of Error".
- Hank Scorpio, a one-off character who was a Bond villain whose gimmick was caring greatly for his employees. He was such a popular character that the writers considered bringing him back for The Simpsons Movie, but ultimately decided against it because they felt they wouldn't be able to do his character justice.
- Both Troy McClure and Lionel Hutz - voiced perfectly by the late Phil Hartman - deserve a mention as well, especially the former - before Hartman's death, there were talks about a potential live action film featuring the character. It can't be just a coincidence that the retirement of both characters coincides with the point in the show's history when it developed a Broken Base.
- Edna Krabappel certainly stands out among the show's guest-voiced characters, possibly outshining even Phil Hartman's Classic Era icons Lionel Hutz and Troy McClure. She was much beloved by fans for her strong personality, relatable troubles, iconic bits (including a few Pet the Dog moments from and towards her), and engaging "frenemy" relationship with Bart Simpson (some enjoy her for her Ms. Fanservice moments too). Many rooted for her to one day find the happy relationship she sought so desperately throughout the show, and her actress Marcia Wallace received tons of praise for her voicework as Krabappel. The massive outpouring from both fans and staff following the death of Marcia Wallace and the subsequent retirement of Krabappel from the series (including some major Tear Jerker moments from the show) speaks volumes about the character's popularity, and many are glad she got the ending she deserved after becoming Happily Married to Ned Flanders.
- Seymour Skinner. He's a Fountain of Memes, shows several moments of genuine badassery, has a backstory that straddles the line between hilarious and tragic, has an entertaining Friendly Rivalry with Bart Simpson, and thanks to his deep voice and Adorkable qualities, has garnered a sizable Estrogen Brigade. In fact, the collective meltdown over the reveal that he was an imposter impersonating the real Seymour Skinner caused a lot of people to give up on The Simpsons and declare that moment as "the moment it stopped being good".
- Bleeding Gums Murphy only had a major role in two episodes and a number of background appearances in-between these before his character's death, but his role as a kindred spirit and mentor to Lisa is fondly remembered by older fans of the show (especially those who watched the first season). His death was one of the show's truest Tear Jerker episodes.
- Professor Frink was introduced as a wacky Mad Scientist character who wanted funding for his death ray—which Grandpa Simpson talked him out of developing without even trying. He quickly became a regular character. He even had a website dedicated to him before FOX had it removed.
- Disco Stu was originally just a one-shot character meant as a joke. Homer was selling a custom-made rhinestone jacket at a yard sale that said "Disco Stu" on the back. When Marge asked who it was, Homer replies "Well, it was supposed to say 'Disco Stud' but I ran out of space." He was well-received enough to be promoted to a regular recurring character.
- Cletus the Slack-Jawed Yokel was originally created for a quick joke in an early episode, but proved popular enough with fans that he was made into a series regular, even being given a surname (Spuckler), a wife, numerous children (one of whom was even a Love Interest to Bart), an entire extended family, and even several episodes in which he and his family plays a large role or even take center stage.
- Gerald Sampson, the unibrowed baby who is Maggie's rival is fairly popular with the fandom despite his minimal roles, as he often proves quite memorable when he does appear and has also given some fuel for the shippers as Maggie's future husband.
- The late Frank Grimes (Or "Grimey" as he liked to be called) appeared in only one episode and yet is one of the most memorable Simpsons characters ever.
- Groundskeeper Willie has numerous priceless moments and is easily a major fan favorite (especially among Scottish viewers). He appears fairly regularly, but he had to wait till the 17th season to have an episode which would focus on him.
- Lenny, for being a regular Butt-Monkey, his obsession with Carl, and often bizarre quirks.
- Out of any one-timer children, Allison Taylor from "Lisa's Rival" and Jessica Lovejoy from "Bart's Girlfriend" are possibly tied for having the most fans. While they've both been Demoted to Extra with only non-speaking cameos since their particular episodes, they're often play much bigger roles in fanworks.
- Smithers has gained quite a bit of popularity for some time now due to traits including being considered the perfect way to complete Burns and his arguably adorkable vibe.
- Leon Kompowsky is fondly remembered by fans for being voiced by the late Michael Jackson.
- And of course, there's Rick Sanchez and Morty Smith, not bad for only showing up for a quick crossover Couch Gag!
- From the arcade game, the giant Bowling Ball you fight in level 6 has gained it's share of fans thanks to it's unique design and attacks. Someone even made it a playable character
in M.U.G.E.N. - Karl, Homer's gravel-voiced note , hyper-competent personal assistant in "Simpson and Delilah", whose dedication, savviness and Straight Gay qualities made him a very memorable one-off character.
- Hans Moleman is very popular due to being the subject of many the most memorable and hilarious moments in the series, such as the "Man Getting Hit By Football" film. He's also possibly the biggest Butt-Monkey in Springfield, which is saying a lot.
- Superintendent Chalmers has been gaining popularity in recent years due to the frequently quoted and memetic "Skinner and the Superintendent" sketch from "22 Short Films About Springfield". He's also well-liked for being a good foil to Principal Skinner as well as being one of the few sane Springfield citizens.
- Ruth Powers and her daughter Laura, the Simpsons' rarely-seen other neighbors introduced in "New Kid on the Block", are pretty popular with fans. Laura only appeared in their debut episode and Ruth's only other role of significance was "Marge on the Lam", but many fans have expressed interest in seeing more of them, owing to their memorable friendships with Bart and Marge respectively.
- Herb Powell, Homer's half-brother, is a fairly popular character, due to his Cool Uncle status to the Simpson family and complex relationship with Homer, on top of being voiced by Danny DeVito.
- Mr. Bergstrom, Lisa's Cool Teacher from "Lisa's Substitute" who encouraged her to be who she was has gained many fans from his one appearance. Being portrayed by Dustin Hoffman (who was credited as "Sam Etic") certainly helped.
- Dolph Starbeam, specifically because he's received far less focus and characterization than his friends Jimbo and Kearny despite being one of the longest running characters in the show.
- Ian the Very Tall Man from "22 Short Films About Springfield" has developed a small but noticeable following for his very memorable scene at the end of the episode in which he gives Nelson Muntz some massive Laser-Guided Karma for constantly mocking everyone else's misfortune.
- As reviled as "The Principal and The Pauper" is, Martin Sheen's portrayal of the real Skinner is generally considered a way to use a guest star right.
- Cecil Terwilliger, Sideshow Bob's even more murderous brother, appearing in "Brother From Another Series", is quite popular among fans thanks to his hilarious chemistry with Bob coming from both actors also being brothers in Frasier, and being a surprisingly threatening yet still laughably charming villain in his own right. His popularity likely allowed him to make a reappearance in a much later episode, "Funeral For a Fiend". Even those who don't like or don't care for Sideshow Bob's family at least like Cecil.
- Even the writing staff has at least three darkhorses: John Swartzwelder (noted for both his distinct brand of absurd non-sequitur-based comedy (to the extent where lines and concepts penned by him remain visible within the finished episodes of a show noted for extensively editing its staff's scripts) and his astonishing written episode count, having entirely or partially penned 59 of the show's first 318 episodes from 1989-2003), George Meyer (noted for both defining the show's comedic sensibilities via his own biting, macabre and concise sense of humour and the longevity of his tenure, having served as a lead creative force on the series for the majority of its first twelve seasons, followed by a more cursory role in seasons 13-16), and especially Conan O'Brien, despite the latter having only worked on the show for a little over one season.
- The unnamed Canadian father from "Bart on the Road" is well-liked for his brief yet memorable dialogue and his "That's it! Back to Winnipeg!" creating a minor meme.
- Mr. Burns' poorly-conceived alias "Mr. Snrub" from "Marge vs. The Monorail" is quite popular, even to the point that its has becoming a Running Gag in the fandom to insist that he's his own character separate from the Power Plant owner.
- Kang and Kodos are always considered highlights of the already beloved Treehouse of Horror episodes, whether they’re the focus or just cameos, they have many fans who always look forward to seeing them every Halloween. They’re popular enough that they even managed to appear in a few non-Halloween episodes as well.
- Leopold, Superintendent Chalmers' hulking and angry henchman that the children of Springfield Elementary are terrified of (in spite of him only there to introduce other characters). Even through his limited appearances, he makes the most out of any time he's onscreen.
- Dr. Wendy Sage, the hypnotherapist, has gotten a surprising amount of praise from fans for being a breast cancer survivor—just in time for Breast Cancer Awareness Month, even.
- Samantha Stanky, Milhouse's one-time girlfriend from "Bart's Friend Falls In Love". She was cute as a button, genuinely loved Milhouse and even forgave Bart when he broke them up and got her sent away to a Catholic boarding school, but she was only seen in that episode.
