The Law & Order of Great Britain, Doctor Who is peppered with famous faces. But often hidden behind impressive makeup or a gaudy costume, some celebs are easy to miss (don’t blink!).Karen Gillan (Amy Pond) and Peter Capaldi (Twelfth Doctor) now-infamously appeared in one episode of the show (“The Fires of Pompeii”) before snagging headlining roles.Check out our list of 20 A-list guest stars. Who knows, maybe one will become the next Doctor.Simon PeggVia Photographer: Gage SkidmoreWho he plays: The Editor in “The Long Game” (season 1, episode 7)Where you’ve seen him: 14 brilliant episodes of Spaced, Edgar Wright’s Three Flavors Cornetto Trilogy, the latter three Mission: Impossible films, Scotty in the Star Trek reboot.Best quote: “For almost a hundred years, mankind has been shaped and guided, his knowledge and ambitions strictly controlled by its broadcast news, edited by my superior, your master, and humanity’s guiding light, the Mighty Jagrafess of the Holy Hadrojassic Maxarodenfoe.” [pause] “I call him Max.”Anthony Stewart HeadVia Photographer: Raven UnderwoodWho he plays: Mr. Finch in “School Reunion” (season 2, episode 3)Where you’ve seen him: Buffy Summers’ enchanting mentor/surrogate father Rupert Giles in Buffy the Vampire Slayer, Uther Pendragon in Merlin.Best quote: “Forget the shooty dog thing.”Andrew GarfieldVia Photographer: Gerald GeronimoWho he plays: Frank in “Daleks in Manhattan” (season 3, episode 4) & “Evolution of the Daleks” (season 3, episode 5)Where you’ve seen him: The Social Network, The Amazing Spider-Man 1 & 2, formerly on Emma Stone’s arm.Best quote: “We gotta stick together. It’s easy to get lost. It’s like a huge rabbit warren. You could hide an army down here.”Mark GatissBBCWho he plays: Professor Richard Lazarus in “The Lazarus Experiment” (season 3, episode 6) & Gantok (as Rondo Haxton) in “The Wedding of River Song” (season 6, episode 13)Where you’ve seen him: The League of Gentlemen, Starter for 10, Wolf Hall, Mycroft Holmes in Sherlock (which he co-created (with Who showrunner Steven Moffat), writes, and stars in).Fun fact: Gatiss not only wrote eight episodes of Doctor Who, but also provided the voice of Danny Boy in “Victory of the Daleks” (season 5, episode 3) and “A Good Man Goes to War” (season 6, episode 7). Plus, he wrote An Adventure in Space and Time, the 2013 TV movie dramatisation of the creation of Doctor Who.Best quote: “One lifetime’s been too short for me to do everything I’d like. How much more I’ll get done in two, or three, or four.”Harry LloydVia Photographer: Rich HardcastleWho he plays: Baines/Son of Mine in “Human Nature” (season 3, episode 8) & “The Family of Blood” (season 3, episode 9)Where you’ve seen him: Viserys Targaryen in Game of Thrones, The Iron Lady, The Theory of Everything, Wolf Hall.Best quote: “Have you enjoyed it, Doctor? Being human? Has it taught you wonderful things? Has it made you better? Richer? Wiser?”Carey MulliganBBC AmericaWho she plays: Sally Sparrow in “Blink” (season 3, episode 10)Where you’ve seen her: An Education, Never Let Me Go (with Andrew Garfield), The Great Gatsby, Inside Llewyn Davis, Far from the Madding Crowd.Best quote: “Don’t take your eyes off that.”Kylie MinogueVia Photographer: Renan KatayamaWho she plays: Astrid Peth in “Voyage of the Damned” (2007 Christmas special)Where you’ve seen her: Minogue was a pop star in the US, but Down Under she gained fame in Australian soap Neighbours, and has acted in Moulin Rouge, and other forgettable films and TV shows.Best quote: “You’re looking good for 903.”Colin MorganBBCWho he plays: Jethro in “Midnight” (season 4, episode 10)Where you’ve seen him: Merlin (with Anthony Head), The Fall, Humans.Best quote: “Maybe we’ve broken down. … In the middle of nowhere.”David MorrisseyVia Photographer: Gage SkidmoreWho he plays: Jackson Lake in “The Next Doctor” (2008 Christmas special)Where you’ve seen him: The Other Boleyn Girl, The Walking Dead, The Missing.Best quote: “There she is. My transport through time and space. The TARDIS! … T-A-R-D-I-S. It stands for Tethered Aerial Release Developed in Style!”Brian CoxBBCWho he plays: voice of Elder Ood in “The End of Time: Part 1” (2009 Christmas special)Where you’ve seen him: Everywhere: Rob Roy, Braveheart, The Long Kiss Goodnight, Rushmore, For Love of the Game, The Rookie, The Bourne Identity, The Ring, Adaptation, 25th Hour, The Reckoning, X-Men 2, Troy, Match Point, Red Eye, Deadwood, Running With Scissors, Zodiac, RED, Rise of the Planet of the Apes, RED 2, Pixels, The Carer (actually, you’ve probably not seen him in that last one, but you definitely should).Fun fact: Cox also starred as a BBC exec in An Adventure in Space and Time, the 2013 TV movie dramatisation of the creation of Doctor Who.Best quote: “Events that have happened are happening now.”Timothy DaltonNBCWho he plays: The Narrator in “The End of Time: Part 1” (2009 Christmas special) & Lord President in “The End of Time: Part 2” (2010 New Year’s special)Where you’ve seen (and heard) him: James Bond in The Living Daylights and License to Kill, Hot Fuzz (with Simon Pegg), Toy Story 3, Chuck, Penny Dreadful.Best quote: “And so it came to pass, on Christmas Day, that the human race did cease to exist. … For this was far more than humanity’s end. This day was the day upon which the whole of creation would change forever. This was the day the Time Lords returned. For Gallifrey.”Bill NighyVia Photographer: flickr.com/alotofmillionWho he plays: Dr. Black in “Vincent and the Doctor” (season 5, episode 10)Where you’ve seen him: Still rocking in Love Actually, Three Flavors Cornetto Trilogy (with Simon Pegg), the first two Pirates of the Caribbean films, Harry Potter and the Deathly Hallows (with Michael Gambon), About Time, The Second Best Exotic Marigold Hotel.Best quote: “To my mind, that strange, wild man who roamed the fields of Provence was not only the world’s greatest artist, but also one of the greatest men who ever lived.”James CordenCBSWho he plays: Craig in “The Lodger” (season 5, episode 11) & “Closing Time” (season 6, episode 12)Where you’ve seen him: Before he was singing carpool karaoke on late night, Corden starred in The History Boys, Gavin & Stacey, Gulliver’s Travels, Into the Woods, The Wrong Mans, and won a Tony for the Broadway play One Man, Two Guvnors.Best quote: “You’ve noticed something. You’ve got your noticing face on. I have nightmares about that face.”Michael GambonBBCWho he plays: Kazran Sardick/Elliot Sardick in “A Christmas Carol” (2010 Christmas special)Where you’ve seen (and heard) him: Toys, The Insider, Sleepy Hollow, Gosford Park, The Life Aquatic with Steve Zissou, The King’s Speech, Hail, Caesar!, Albus Dumbledore (replacing the late Richard Harris) in the latter six Harry Potter films.Fun fact: Gambon also voiced the Ghost of Christmas Present in the 2001 animated film “Christmas Carol: The Movie.”Best quote: “On every world, wherever people are, in the deepest part of the winter, at the exact midpoint, everybody stops, and turns, and hugs, as if to say ‘Well done. Well done, everyone! We’re halfway out of the dark.’ Back on Earth, we called this Christmas, or the Winter Solstice. On this world, the first settlers called it the Crystal Feast. You know what I call it? I call it expecting something for nothing.”Mark SheppardThe CWWho he plays: Canton Delaware in “The Impossible Astronaut” (season 6, episode 1) & “Day of the Moon” (season 6, episode 2)Where you’ve seen him: Firefly, 24, Romo Lampkin in Battlestar Galactica, Dollhouse, Chuck, White Collar, Crowley in Supernatural.Best quote: “That’s OK. You were my second choice for president, Mr. Nixon.”Hugh BonnevilleBBCWho he plays: Henry Avery in “The Curse of the Black Spot” (season 6, episode 3)Where you’ve seen him: Notting Hill, Mansfield Park, Paddington, W1A, Robert Crawley, Earl of Grantham in Downton Abbey.Best quote: “To the rigging, you dogs! Let go the sails! Avast ye! Put the bunt into the slack of the clews!”Michael SheenVia Photographer: Gage SkidmoreWho he plays: Voice of House in “The Doctor’s Wife” (season 6, episode 4)Where you’ve seen him: The Queen, Frost/Nixon, three films in that series which shall not be named (The Twilight Saga), 30 Rock, Midnight in Paris, Far From the Madding Crowd (with Carey Mulligan), Dr. William Masters in Masters of Sex, Passengers.Best quote: “Fear me. I’ve killed hundreds of Time Lords.”David BradleyVia Photographer: Gage SkidmoreWho he plays: Solomon in “Dinosaurs on a Spaceship” (season 7, episode 2)Where you’ve seen him: Argus Filch in every Harry Potter film, Broadchurch (with the 10th Doctor, David Tennant), Game of Thrones.Fun fact: Bradley also portrayed first Doctor William Hartnell in An Adventure in Space and Time, the 2013 TV movie dramatisation of the creation of Doctor Who (with Brian Cox, written by Mark Gatiss).Best quote: “Do you hear that? Did you hear what he called him? Doctor. After all this time. Bring them to me.”Ian McKellenVia Photographer: Steve PunterWho he plays: Voice of Great Intelligence in “The Snowmen” (2012 Christmas special)Where you’ve seen him: David Copperfield (TV series), Richard III, Eric Lensherr/Magneto in X-Men 1-3 & spin-off movies, Gandalf in The Lord of the Rings 1-3 & The Hobbit 1-3.Best quote: “Now the dream outlives the dreamer and can never die.”Nick FrostVia Photographer: Gage SkidmoreWho he plays: Santa Claus in “Last Christmas” (2014 Christmas special)Where you’ve seen him: See Simon PeggBest quote: “Oh, sorry about this, girl. We… We are just three passing, perfectly ordinary roof people, doing some emergency roof things.” Stream Doctor Who here for free with your Amazon Prime account.