15 Most Unforgettable 'The Simpsons' Guest Stars

1. Michael Jackson in "Stark Raving Dad" (1991)

When you have the King of Pop voicing a mental institution patient who thinks he's... well, Michael Jackson, you know you're in for an eccentric ride. Leon Kompowsky was his name and spreading cheer was his game. Despite the legal shenanigans that required Jackson to go uncredited and have a singing double, his speaking voice alone made the character both soothing and intriguing. He helped Bart compose a birthday song for Lisa that still gives fans all the feels. It was a thriller performance indeed.

2. Stephen Hawking in "They Saved Lisa's Brain" (1999)

You'd think having the world's most renowned physicist guest star in a cartoon would be a scholarly affair. But nope, this is "The Simpsons," folks! Hawking appears as a patron in Moe's Tavern, sports a helicopter attachment for his wheelchair, and forms an unusual bond with Homer. He saved Lisa from the pseudo-intellectuals of Springfield, delivering his lines with robotic brilliance. His humor, mixed with astute observations about the absurdity of Springfield, made his performance a gravitational pull.

3. Kelsey Grammer as Sideshow Bob Terwilliger (Multiple episodes)

Cheers to one of the most recurring guest stars, Kelsey Grammer, whose portrayal of Sideshow Bob is arguably as iconic as Frasier Crane. He's Bart's sophisticated, erudite, and slightly unhinged nemesis, with a vendetta as enduring as Homer's love for beer.

Each of his melodramatic monologues, often peppered with Shakespearean flair, adds a delicious layer of complexity to the world of Springfield. From "Krusty Gets Busted" to "Bobby, It's Cold Outside," his performances are a lyrical delight, proving comedy and culture can co-exist, even in cartoons.

4. Leonard Nimoy in "Marge vs. the Monorail" (1993)

Who better to attend Springfield's monorail inauguration than Star Trek's own Mr. Spock? Nimoy brings his signature brand of deadpan humor and charming self-mockery, making numerous references to his Star Trek fame. The absurdity of Nimoy narrating his 'adventures' to the disinterested monorail driver culminates in him claiming credit for saving the day, making this one of the most hilariously memorable guest appearances.

5. Elizabeth Taylor in "Lisa's First Word" (1992)

Elizabeth Taylor, a legend in her own right, had the honor of uttering arguably the most famous single word in Simpsons history – "Daddy." That's right, she voiced the rarely verbal Maggie Simpson in this emotionally charged episode. The Hollywood icon recording multiple takes of a single word to get the perfect infant pronunciation is a testament to her dedication. Her one word still resonates as one of the series' most endearing moments.

6. Paul McCartney in "Lisa the Vegetarian" (1995)

Only a Beatle could convince Lisa to stick with vegetarianism, right? Paul and Linda McCartney made a memorable cameo in this food-centric episode. Paul's insistence that playing a song backwards reveals a recipe for lentil soup is a gem of a moment. The McCartneys not only lent their voices but brought their real-life commitment to animal rights to the heart of Springfield. Paul's timeless cool added an extra flavor to Lisa's transformative journey.

7. Johnny Cash in "The Mysterious Voyage of Homer" (1997)

When a hallucination-gone-wild episode needed a voice for a space coyote (don't ask), who better to call than the Man in Black himself? Johnny Cash brings his deep, soulful voice to guide Homer through a psychedelic trip, triggered by an absurdly hot chili pepper. Cash's hypnotic tone gave the space coyote an enigmatic charm and an air of wisdom, making his one-off character a key guide in Homer's self-discovery journey.

8. Michelle Pfeiffer in "I'm with Cupid" (1999)

When Moe falls head over heels in love, he doesn't mess around. Michelle Pfeiffer voiced his love interest, Renee, in this romantic yet hilariously tragic episode. Pfeiffer's sultry voice and smooth delivery made Renee the perfect object of Moe's affection. From Moe's extravagant Valentine's Day gestures to his eventual heartbreak, Pfeiffer's nuanced portrayal made this episode one of the most memorable of Moe's many romantic misadventures.

9. Mark Hamill in "Mayored to the Mob" (1998)

"Use the forks, Luke!" Mark Hamill's appearance as himself, moonlighting as a dinner theatre actor while promoting Sprint, is a delightful mashup of meta-humor and Star Wars references. His frantic acting lessons with Homer and his indignant insistence that he's not just Luke Skywalker make for a hysterical guest spot. It's a joyful love letter to Star Wars fans and a showcase of Hamill's comedic timing.

10. Danny DeVito as Herb Powell (Multiple episodes)

Danny DeVito as Homer's successful, long-lost half-brother Herb Powell brought a new dynamic to the Simpson family. From being a millionaire to becoming homeless because of Homer's disastrous car design, DeVito's Herb was an emotional roller coaster. His voice work combined frustration, despair, and familial warmth that made Herb's character arc both hilarious and touching. DeVito's return in "Brother, Can You Spare Two Dimes?" was a welcomed encore.

11. Patrick Stewart in "Homer the Great" (1995)

Springfield's Stonecutters society wouldn't be complete without Captain Picard, I mean, Patrick Stewart, at its helm. Stewart, as Number One (see what they did there?), brought his iconic voice to guide Homer through the secret society's ludicrous rituals and sing-alongs. Watching him deliver the absurdity with utter seriousness, like a Shakespearean drama, is worth its weight in donuts.

12. Glenn Close as Mona Simpson (Multiple episodes)

When your long-lost mom is a Hippie-turned-fugitive, only Glenn Close could bring the necessary verve to the role. Close's portrayal of Mona Simpson, Homer's mother, is a riotous blend of sixties counterculture and maternal warmth. Mona's radical past, daring escapes, and the emotional impact she leaves on the Simpson family each time she disappears, make her a recurring character we love to welcome back. Close's voice work is as dynamic as Mona's hairstyles, making each appearance a delight.

13. Alec Baldwin and Kim Basinger in "When You Dish Upon a Star" (1998)

Hollywood royalty lands in Springfield, with Alec Baldwin and Kim Basinger playing themselves as Homer's new best buddies (in his head, at least). The couple's attempt at a quiet life in Springfield, from dealing with Homer's ridiculous script ideas to his eventual betrayal, is a comedy of errors. The duo brought charm and humility to their caricatures, turning a satirical jab at Hollywood into an amusingly memorable episode.

14. Ron Howard in "When You Dish Upon a Star" (1998) & "Children of a Lesser Clod" (2001)

Speaking of Hollywood, let's not forget Opie himself, Ron Howard. After making an appearance alongside Baldwin and Basinger, Howard reappears in a later episode to pitch one of Homer's ridiculous movie ideas. His willingness to poke fun at himself, coupled with his spot-on comedic timing, turns both episodes into riotous Hollywood satires that keep fans coming back for more.

15. The Ramones in "Rosebud" (1993)

Punk rock in Springfield? You bet! The Ramones playing "Happy Birthday" to Mr. Burns is as wonderfully bizarre as it sounds. The band's raucous performance at Mr. Burns's birthday bash, followed by their snarky quip, "Go to hell, you old bastard," is a perfect encapsulation of the band's rebellious spirit. The Ramones rocked their cameo, proving Springfield can handle punk just as well as it can handle pop.