For its 100th episode Tuesday night, "Glee" pretty much will do as it's done in all its previous episodes: It'll boast a special guest star. (On Tuesday, actually, it'll boast two special guest stars — Gwyneth Paltrow and Kristin Chenoweth.)
In honor of the show-choir show's centennial, here's a rundown of the top "Glee" guest stars, a not-small collection of performers who've bravely pitted their vocals against those of the kids from New Directions.
1. Kristin Chenoweth
Known outside of "Glee" as: The Emmy-winning TV actress, and Broadway star of "Wicked."
Known on "Glee" as: April Rhodes, the talented but messed-up former McKinley High classmate of New Directors adviser Will Schuester (Matthew Morrison).
First appearance: "The Rhodes Not Taken," from Season 1, when the show was young and famous people weren't yet in the habit of turning up on it.
Stunt casting or superb casting? Chenoweth was the first "Glee" special guest star, and, judging by the fact that she's been booked for the 100th episode, she's still one of the best.
Signature song: The "Cabaret" showstopper "Maybe This Time," as belted out in the show-choir room along with Rachel (Lea Michele). It's one of those do-gooding "Glee" moments when the show introduces its largely young audience to the Great American Songbook and does it spectacularly well.
2. Jonathan Groff
Known outside of "Glee" as: The Broadway star ("Spring Awakening," co-starring Michele) and, more recently, the TV star of HBO's "Looking."
Known on "Glee" as: Jesse St. James, the hot, naughty rival of Finn (Cory Monteith) and all of New Directions.
First appearance: "Hell-O," from Season 1.
Stunt casting or superb casting? Groff presumably wasn't the biggest name "Glee" could've landed for Vocal Adrenaline's St. James, but his talent and backstory with Michele make him a delicious roadblock for the early days of Finn and Rachel.
Signature song: It's hard to choose. Is it "Hello," a duet with Michele that makes you sorry for ever thinking of the Lionel Richie song as cheesy? Or is it "Rolling in the Deep," another duet with Michele that makes you wonder if it's better than the Adele original?
3. Olivia Newton-John
Known outside of "Glee" as: The world-famous pop star.
Known on "Glee" as: The world-famous pop star.
First appearance: "Bad Reputation," from Season 1.
Stunt casting or superb casting? Not that it's not fun to watch Jane Lynch in a musical number, but this is stunt casting all the way. It's worth noting that Newton-John is fun to watch, too, and that stunt casting does not necessarily mean bad casting. In this instance, however, it does indicate that "Glee" will soon be far, far away, in terms of tone, from its earnest pilot.
Signature song: A redo of Newton-John's aerobic hit, "Physical," with cheer-coach Sue Sylvester (Jane Lynch).
4. Neil Patrick Harris
Known outside of "Glee" as: The dapper star of "How I Met Your Mother" and host of award shows everywhere.
Known on "Glee" as: Bryan Ryan, the weaselly rival of Mr. Schuester.
First appearance: "Dream On," from Season 1.
Stunt casting or superb casting? You can't go wrong with Harris, and "Glee" doesn't.
Signature song: "Dream On," natch, an over-the-top, fantastic sing-off between Will and Bryan Ryan.
5. Idina Menzel
Known outside of "Glee" as: The one and only, "Wicked"-ly talented "Adele Dazeem."
Known on "Glee" as: Shelby Corcoran, the adviser of Vocal Adrenaline who has a secret (she's Rachel's birth mother).
First appearance: "Hell-O," from Season 1.
Stunt casting or superb casting? Perfect casting, actually. It takes a Broadway-caliber talent to spawn a Broadway-caliber talent.
Signature song: As a recurring character, Menzel has belted out several numbers, but her "Poker Face" duet with Michele best defines her relationship with her TV daughter. At the same time, it redefines the Lady Gaga song. Who knew it worked as a piano ballad?
Known outside of "Glee" as: The YouTube-discovered Filipina pop star.
Known on "Glee" as: The sweet kid with the killer voice, Sunshine Corazon.
First appearance: "Audition," from Season 2.
Stunt casting or superb casting? A little bit of both, maybe, but it works.
Signature song: "Listen" makes Sunshine's statement to New Directions (just before she defects to Vocal Adrenaline), but our pick here goes to "Telephone," another Lady Gaga song that "Glee" does very right, thanks to Charice and Michele.
7. John Stamos
Known outside of "Glee" as: "Full House's" Uncle Jesse-turned-venerable actor and all-around hot guy.
Known on "Glee" as: Dr. Carl Howell, romantic rival of Will Schuester and all-around hot dentist.
First appearance: "Britney/Brittany," from Season 2.
Stunt casting or superb casting? Even if the role didn't require the occasional singing or stint behind the drums (as it does on "Afternoon Delight"), Stamos would still be just the right good-looking man to come between Will and Emma (Jayma Mays).
Signature song: "Whatever Happened to Saturday Night?," the Meat Loaf number from "The Rocky Horror Picture Show" as rolled out in the "Glee" episode "The Rocky Horror Glee Show."
8. Gwyneth Paltrow
Known outside of "Glee" as: The arguably insufferable Oscar-winning actress and lifestyle guru.
Known on "Glee" as: The thoroughly refreshing substitute teacher Holly Holliday.
First appearance: "The Substitute," from Season 2.
Stunt casting or superb casting? Paltrow's a big "get," certainly, but until you see her in action, you couldn't have guessed she could be so loose and funny and just right for the "Glee" universe. So many of the show's best moments are her moments, from the rousing "Nowadays/Hot Honey Rag" duet with Michele's Rachel to the affecting "Landslide" with lovestruck Cheerios Santana (Naya Rivera) and Brittany (Heather Morris). In the show's 100th episode, she elevates Pharrell Williams's "Happy" to a new level of bright and sunny.
Signature song: "Forget You," the winning redo of the CeeLo Green hit made even that much more winning by Paltrow's robot dance moves.
9. Carol Burnett
Known outside of "Glee" as: The beloved comedy and variety performer.
Known on "Glee" as: Doris, the harsh taskmaster of a mother to Sue Sylvester.
First appearance: "Furt," from Season 2.
Stunt casting or superb casting? Once again, it's a little of both. At this point in "Glee's" run, the show wasn't going to cast a no-name as Sue's mother. Fortunately, it found a legend up for the challenge.
Signature song: "Ohio," the old Broadway comic lament (from "Wonderful Town")-turned-duet for Doris and Sue.
10. Ricky Martin
Known outside of "Glee" as: The charismatic "Livin' la Vida Loca" guy.
Known on "Glee" as: David Martinez, the charismatic night-school Spanish teacher guy.
First appearance: "The Spanish Teacher," from Season 3.
Stunt casting or superb casting? Martin is perfectly fine, but his stint suffers for occurring when "Glee" seemed fresh out of ideas on how to keep Mr. Schuester relevant.
Signature song: "Sexy and I Know It" was not written for Martin (it was written for LMFAO), but it could have been.
11. Matt Bomer
Known outside of "Glee" as: The GQ-handsome star of "White Collar."
Known on "Glee" as: Cooper Anderson, the GQ-handsome older brother of Blaine (Darren Criss).
First appearance: "Big Brother," from Season 3.
Stunt casting or superb casting? Just as Martin is perfectly fine, Bomer is perfectly fine. As Blaine's brother, in fact, he's pretty perfect. The problem is that Season 3 "Glee" has so many characters, it hardly needs another one to do a Lima, Ohio stopover.
Signature song: "Somebody That I Used to Know," the Gotye hit that serves as an appropriate soundtrack for sibling rivalry.
12. Kate Hudson
Known outside of "Glee" as: The chick-flick heroine of "How to Lose a Guy in 10 Days," "Raising Helen," and "Bride Wars."
Known on "Glee" as: Cassandra July, the exacting dance teacher a la "Fame."
First appearance: "The New Rachel," from Season 4.
Stunt casting or superb casting? The Debbie Allen role is so against Hudson's spunky type that the actress's mastery of it qualifies as a personal win. Now, whether the show's New York-Lima split story lines, which debuted in Season 4, work is another story.
Signature song: "Americano/Dance Again" is so good, it reminds you that you need to check out Hudson in "Nine," even if the 2009 big-screen musical itself isn't very good.
13. Sarah Jessica Parker
Known outside of "Glee" as: Fashion icon Carrie Bradshaw from "Sex and the City."
Known on "Glee" as: Isabelle Wright, the fashionable Vogue.com boss of Kurt (Chris Colfer).
First appearance: "Makeover," from Season 4.
Stunt casting or superb casting? Ridiculous casting. A nobody kid from Ohio deplanes in Manhattan and almost immediately lands a loft apartment and a topflight job with a topflight editor? Please. Again, the problem isn't the actor; it's the storyline.
Signature song: Parker revisits her "Annie" past with the mashup "The Way You Look Tonight/You're Never Fully Dressed Without a Smile."
14. Demi Lovato
Known outside of "Glee" as: The Disney Channel star of "Sonny With a Chance" and "Camp Rock."
Known on "Glee" as: The waitress and Santana love interest, Dani.
First appearance: "Tina in the Sky With Diamonds," from Season 5.
Stunt casting or superb casting? It probably didn't hurt that Lovato joined the cast after she'd joined the judges' table on "The X Factor," which, like "Glee," is a Fox show. But her sunny performance nonetheless gives a good name to corporate synergy.
Signature song: "Here Comes the Sun," a duet between (and jumping-off point for) Dani and Santana.
15. Adam Lambert
Known outside of "Glee" as: Glam-style rocker and Season 8 runner-up on "American Idol."
Known on "Glee" as: Glam-style rocker Elliott Gilbert, aka Starchild.
First appearance: "A Katy or a Gaga," from Season 5.
Stunt casting or superb casting? Lambert debuted on "Glee" in an impossible situation: namely, the immediate aftermath of the show's emotional farewell to Finn, whose portrayer Monteith died in 2013. Where once Lambert's bombast might've seemed like a kick, it now felt too loud and too jarring, even on a show marked by wild swings.
Signature song: A blow-out-the-lights version of Lady Gaga's "Marry the Night."
16. Skylar Astin
Known outside of "Glee" as: The cute, nice guy in the a cappella choir comedy "Pitch Perfect."
Known on "Glee" as: Jean Baptiste, the cute, jerky guy from the rival show choir Throat Explosion.
First appearance: "City of Angels," from Season 5.
Stunt casting or superb casting? Pitch-perfect, of course.
Signature song: A Throat Explosion mashup of "Mr. Roboto" and "Counting Stars."
"Glee" airs Tuesdays at 8 p.m. on Fox.