When it comes to talking about characters seen on guest stars, and many more. While many of those fields have their day in the sun, the recurring characters can get overlooked, which is unacceptable, considering their caliber of humor.
The recurring characters have a lot of flexibility regarding their shenanigans and can fill in gags on an "as needed" basis. Here's a ranking of 10 of the best all-time recurring characters on The Simpsons.
Duffman
"Hey, it's Duffman! The guy in a costume that creates awareness of Duff!" There could not have been a better introduction to a character, and the deliverance of such a straightforward line from Lenny makes it all the funnier. Duffman is a jock in a Duff costume who...well, creates awareness of Duff, while Yello's "Oh Yeah" song plays (famously used in Ferris Bueller's Day Off).
Perhaps what makes Duffman even funnier is that Brad Bird physically re-created the ridiculous Duffman pelvic thrusts while pitching the idea, according to the DVD commentary. Truly, the man is a master of animation with a lot of dedication.
Rainier Wolfcastle
Wolfcastle is one of the many characters in the show based loosely on a real-life person, such as Mayor Quimby being JFK, or Herman's voice being a Geroge Bush Sr. impression. But Wolfcastle's entire design is much more derivative of his real-life counterpart, Arnold Schwarzenegger.
Wolfcastle's inability to understand humor, properly emote, or get the gist of virtually any aspect of US culture makes him the most masculine fish out of water ever. Maybe it's due to his dedication to bodybuilding or his Hollywood background, but his inability to connect with typical people makes him a priceless mine for laughter. His miniature McBain movie snuck into various episodes of The Simpsons is also one of the show's best Easter eggs.
Ralph Wiggum
Ralph Wiggum is a great character because he is an overblown stereotype, like many of the characters on the show. His exaggerated stupidity, charm, and helplessness make him a bizarre child, but an endearing one. He's Chief Wiggum's son, all right. His simple-minded nature and occasional glimpses of brainpower make him unpredictably dumb or pitiful, and both outcomes always end with laughter.
Fun fact: Ralph is Simpsons creator Matt Groening's favorite character.
Troy McClure
Phil Hartman's presence is greatly missed on The Simpsons, but he left behind a legacy of great joy for everyone to enjoy for the rest of time. Troy McClure would often pop up in random episodes of the show whenever a VHS tape or film-related event was present. You might him from such episodes as "The Simpsons 138th Episode Spectacular" or "A Fish Called Selma."
Troy McClure's downhill slope after starring in B-movies leads him to appear in just about anything, and no matter how brief, the character's inability to be engaging was humorous. When his appearances were larger roles, his Hollywood has-been attitude behind the scenes was scarily accurate.
Disco Stu
Disco Stu is one of the least innovative characters on The Simpsons. He's the prototype version of South Park's "Towelie," a one-time use character who served no real purpose, but mustered love with the writers and became a recurring character.
Disco Stu first appears at a neighborhood yard sale, where Homer's 1970s studded "Disco Stud" jacket has the "D" missing, only for Disco Stu to appear and decide to not buy the jacket so as to not himself. From that point forward, he appears at the most unexpected moments in the show and serves virtually no purpose other than to earn cheap laughs, but laughs nonetheless.
Hans Moleman
Gil Gunderson isn't much of an impressive character, because much of his pathetic humor and hopeless situational comedy is reminiscent of the superior Hans Moleman. Poor Moleman has endured a lot; getting hit in the crotch by a football, alcoholism, a date with Selma, many car accidents, and several deaths (which he always inexplicably returns from).
Hans's bad luck makes him the Mr. Magoo of the show, and his appearances are always over the top and cartoonish, even in an over-the-top cartoon like The Simpsons.
Martin Prince
Poor Martin. He's the kind of kid that even general audiences would probably mock mercilessly if they met in real life. As one of the few intelligent characters in the show, Martin lacks self-awareness, unlike Lisa Simpson.
Throughout the years, in the endless 4th grade, he and Bart have come to find a certain level of neutrality, but he is still hounded by every other bully at Springfield Elementary with extreme prejudice. Martin's teacher's pet behavior, straight-laced attitude, interest in geeky subjects, and incessant need to spew knowledge are what prompt his unfortunate bullying.
Superintendent Chalmers
The "Steamed Hams" segment in The Simpsons is one of the best-known scenes from the entire show's run, and it wouldn't work nearly as well as it does if Superintendent Chalmers wasn't such a suspicious and self-unaware character. For all of the posturing that Principal Skinner does for his boss, Chalmers never appreciates Skinner's attempts to be his best, and always comes for school inspections at the worst moments.
Each time Chalmers appears, the suspense of what's to come and inevitability for disaster is always present, and the appearances only get funnier the more often Chalmers pops up and is forced to play the straight man to Springfield's crazy shenanigans.
Lionel Hutz
Ambulance chasing law-talkin' guys are always a bonus for any comedy, and like Saul Goodman, anytime Lionel Hutz was on screen, he stole the spotlight. Phil Hartman's best character on the show was Lionel Hutz, one of the characters who hit a bullseye with every single one of his jokes.
The character's baffling incompetence, unpredictable attitude, and appearance in extraordinary circumstances made him stick out like a sore thumb in a cast with hundreds of characters to keep track of. The Simpsons never had a better lawyer/babysitter, which is...sad.
Sideshow Bob
The choice to have the sophisticated Sideshow Bob voiced by Kelsey Grammer, hot off his portrayal of Frasier Crane, was one of the best decisions in The Simpsons history. Sideshow Bob is yet another rare intelligent character on the show but has a nasty habit of being a criminal mastermind. After initially appearing in Season 1 after framing his boss, Krusty the Clown, Bob would go onto to become Bart's archnemesis (and occasionally, friend).
Even in later seasons of The Simpsons, where the '90s golden era had long ed, episodes featuring Sideshow Bob remain highlights for fun and madness, and the elegant tone of the character essentially plays like Frasier gone made. An idea reinforced with the fact that Bob's brother and father are voiced by his Frasier co-stars. Sideshow Bob's magnum opus, "Cape Feare," is one of the most universally beloved episodes in the franchise by both fans and critics alike, and even the smallest sliver from Sideshow Bob makes for a memorable appearance. When it comes to the criminal recurring characters, Fat Tony's great, but Sideshow Bob is the most iconic person to fill the role.