The Greatest Guest Appearances on The Simpsons

as Leonard Nimoy

Episodes:
Marge vs. the Monorail (1993)
The Springfield Files (1997)

as Leon Kompowsky

Episodes:
Stark Raving Dad (1991)

as Hank Scorpio

Episodes:
You Only Move Twice (1996)
500 Keys (2011)

as James Woods

Episodes:
Homer and Apu (1994)

as Coyote

Episodes:
El Viaje Misterioso de Nuestro Homer (1997)

Wade Boggs, Jose Canseco, Roger Clemens, Don Mattingly, Steve Sax, Mike Scioscia, Ozzie Smith, Darryl Strawberry, and Terry Cashman as themselves

Episodes:
Homer at the Bat (1992)

as Mr. Bergstrom

Episodes:
Lisa's Substitute (1991)

as John

Episodes:
Homer's Phobia (1997)

as Jessica Lovejoy

Episodes:
Bart's Girlfriend (1994)

as Herb Powell

Episodes:
Oh Brother, Where Art Thou? (1991)
Brother, Can You Spare Two Dimes? (1992)
Changing of the Guardian (2013)

as James Taylor

Episodes:
Deep Space Homer (1994)

as Chester J. Lampwick

Episodes:
The Day the Violence Died (1996)

as Barry White

Episodes:
Whacking Day (1993)
Krusty Gets Kancelled (1993)

as Bleeding Gums Murphy

Episodes:
Moaning Lisa (1990)
'Round Springfield (1995)

as Mel Gibson

Episodes:
Beyond Blunderdome (1999)

as Larry Burns

Episodes:
Burns, Baby Burns (1996)

as The Ramones

Episodes:
Rosebud (1993)

as Ernest Borgnine

Episodes:
Boy Scoutz 'n the Hood (1993)

as Buzz Aldrin

Episodes:
Deep Space Homer (1994)

as Mona Simpson

Episodes:
Mother Simpson (1995)
My Mother the Carjacker (2003)
Mona Leaves-a (2008)
How I Wet Your Mother (2012)

as Adam West

Episodes:
Mr. Plow (1992)

as Dennis Franz playing Homer Simpsons

Episodes:
Homer Badman (1994)

as Stan Lee

Episodes:
I Am Furious Yellow (2002)
Married to the Blob (2014)

as Laura Powers

Episodes:
New Kid on the Block (1992)

as James Brown

Episodes:
Bart's Inner Child (1993)

as Sting

Episodes:
Radio Bart (1992)

as Mindy Simmons

Episodes:
The Last Temptation of Homer (1993)

as Ron Howard

Episodes:
When You Dish Upon a Star (1998)
Hello Gutter, Hello Fadder (1999)

as Stephen Hawking

Episodes:
They Saved Lisa's Brain (1999)
Don't Fear the Roofer (2005)
Stop or My Dog Will Shoot (2007)
Elementary School Musical (2010)

as Neil Patrick Harris playing Bart Simpson

Episodes:
Bart the Murderer (1991)

Ted Danson, Woody Harrelson, Rhea Perlman, and John Ratzenberger as the cast of Cheers

Episodes:
Fear of Flying (1994)

as Bob Newhart

Episodes:
Bart the Fink (1996)

as Karl

Episodes:
Simpson and Delilah (1990)

as Willie Nelson

Episodes:
Behind the Laughter (2000)

as Gary Coleman

Episodes:
Grift of the Magi (1999)
A Tale of Two Springfields (2000)

as The Who

Episodes:
A Tale of Two Springfields (2000)

as Johnny Carson

Episodes:
Krusty Gets Kancelled (1993)

as Mark Hamill

Episodes:
Mayored to the Mob (1998)

as Tom Hanks

Episodes:
The Simpsons Movie (2007)

as Allison Taylor

Episodes:
Lisa's Rival (1994)

as Alex Whitney

Episodes:
Lard of the Dance (1998)

as Elizabeth Taylor

Episodes:
Krusty Gets Kancelled (1993)

as Joe Namath

Episodes:
Bart Star (1997)
Four Regrettings and a Funeral (2013)

and Gillian Anderson as Fox Mulder and Dana Scully

Episodes:
The Springfield Files (1997)

Keith Richards, Elvis Costello, Lenny Kravitz, Tom Petty, and Brian Setzer as themselves

Episodes:
How I Spent My Strummer Vacation (2002)

as Bret 'the Hitman' Hart

Episodes:
The Old Man and the Lisa (1997)

as Malloy

Episodes:
Homer the Vigilante (1994)

as Bob Hope

Episodes:
Lisa the Beauty Queen (1992)

as Robert Goulet

Episodes:
$pringfield (or How I Learned to Stop Worrying and Love Legalized Gambling) (1993)

as Mark McGwire

Episodes:
Brother's Little Helper (1999)