Zoe Wanamaker as Lady Cassandra in "The End of the World"

Harry Potter's Madam Hooch gave voice to one of the new series' first recurring characters. She may have ended her long, long run as a "bitchy trampoline," to quote Rose Tyler (Billie Piper), but Lady Cassandra's story hits all of our favorite Doctor Who tropes: flawed people, falls from grace, and a redemption of sorts.

Penelope Wilton as Harriet Jones in "Aliens of London"

When its not raiding the Harry Potter and Game of Thrones casts, Doctor Who tends to set its sights on Downton Abbey. Before she was the Dowager Countess' frenemesis, Isobel Crawley, Penelope Wilton was Harriet Jones, a British politician turned disgraced prime minister turned dalek-fodder.

Simon Pegg as the Editor in "The Long Game"

You might have to squint to make out Simon Pegg, fresh off Shaun of the Dead, underneath the colored contacts and frosty makeup, but he's there. He's creepy. And he's awesome.

Anne Robinson as Anne Droid in "Bad Wolf"

The Weakest Link host lent her voice to the android host of a homicidal parody of her famous game show.

Pauline Collins as Queen Victoria in "Tooth and Claw"

"The royals are actually werewolves" canon that this early Tenth Doctor outing established never gets old. Pauline Collins, as the perpetually unamused Queen Victoria, is one of a handful of actors who have appeared in both the original run of Doctor Who (as prospective companion Samantha Briggs) and the new series.

Anthony Stewart Head as Brother Lasser in "School Reunion"

In an episode that is notable mostly for a lovely reunion with OG companion Sarah Jane Smith (Elisabeth Sladen) and her robot pupper K-9, we can't ignore the fact that Doctor Who also tapped a Buffy alum, Head, to play a creepy, evil, headmaster as some sort of anti-Giles.

Sophia Myles as Madame de Pompadour in "The Girl in the Fireplace"

Sophia Myles starred as the historical figure Madame de Pompadour in "The Girl in the Fireplace," a wibbly-wobbly, timey-wimey fan-favorite episode notable for creepy Clockwork Droids wearing creepier masks and the Tenth Doctor inventing the banana daiquiri.

Andrew Garfield as Frank in "Daleks In Manhattan"

OMG, look at him. Look at that pre-Spider-Man baby Andrew Garfield, all eager and scrappy to land a job in Depression-era New York City. Unfortunately, what he got was a Dalek cult and... enslaved pig people? This was kind of a weird episode.

Harry Lloyd as Jeremy Baines in "Human Nature"

Harry Lloyd took a break from playing the heroic Will Scarlet on the BBC's Robin Hood to take on the sinister role of Jeremy Baines, an alien whose family was trying to steal the Doctor's essence that he'd locked in a fob watch (don't ask), in Season 3's "Human Nature."

Thomas Brodie-Sangster as Timothy Latimer in "Human Nature"

The little boy from Love Actually who grew up to star in the Maze Runner films and Netflix's Western Godless also appeared in "Human Nature" and its conclusion "The Family of Blood." He played a young boy at the school where the Doctor worked as John Smith while hiding from the Family of Blood. He bonded with the fob watch (again, don't ask).

Carey Mulligan as Sally Sparrow in "Blink" (Season 3)

If you're only going to be in one episode of Doctor Who, it might as well be one of the overwhelmingly beloved, critically acclaimed "great" ones. Season 3's "Blink" saw the introduction of fan favorite baddies the Weeping Angels and sent Carey Mulligan on a quest to save the world... with DVD Easter eggs. It also gave us the phrase "wibbly-wobbly, timey-wimey," and for that we are eternally grateful.

Derek Jacobi as Professor Yana in "Utopia"

Emmy Award winner Sir Derek Jacobi, of pretty-much-all-the-Shakespeare fame, appeared as a scientist trying to save humanity at the end of the universe... only to be revealed as the Doctor's fellow Time Lord and nemesis, the Master, once things went sideways.

Tom Ellis as Tom Milligan in " Last of the Time Lords"

Lucifer star Tom Ellis appeared in the Season 3 finale, also known as Freema Agyeman's final series regular appearance as Martha Jones, as a doctor (not a Doctor) Martha met during the Year That Never Was. He would eventually become her fiancé, though they later called the engagement off.

Kylie Minogue as Astrid Perth in "Voyage of the Damned"

Heroic space-stewardess Astrid helped David Tennant's Doctor save the Earth from its annual Christmas Day space-and-time crisis. She also contributed to the Tenth Doctor's inevitable evolution into a sad emo kid, becoming just a notch on his dead-and-maimed companions bedpost.

Russell Tovey as Midshipman Alonso Frame in "Voyage of the Damned"

Before he was a werewolf on Being Human, Russell Tovey was a midshipman along for the same voyage as Kylie Minogue during the 2007 Christmas special. This is important mostly because his character's name was Alonso, much to the Doctor's delight, but also because he reprised the role for a brief appearance in David Tennant's final episode, when Ten hooked Alonso up with Captain Jack Harkness (John Barrowman).

Sarah Lancashire as Miss Foster in "Partners in Crime"

Most people remember the Season 4 episode "Partners in Crime" because it featured the return of Donna Noble (Catherine Tate) as a full-time companion. But the episode also featured Sarah Lancashire as Miss Foster, a nanny who tricked people into buying a drug they thought led to weight loss but actually just attracted fat cells to transform it into Adipose. Yeah, this episode was weird.

Clive Standen as Private Harris in "The Sontaran Stratagem"

Vikings star Clive Standen appeared as a UNIT soldier in three episodes of Doctor Who's fourth season. He first appeared in "The Sontaran Stratagem" and "The Poison Sky," but then his character popped up in a parallel world in "Turn Left."

Joe Dempsie as Cline in "The Doctor's Daughter"

Game of Thrones star Joe Dempsie appeared as Cline opposite David Tennant's Tenth Doctor in the Season 4 episode "The Doctor's Daughter," which introduced, well, the Doctor's daughter Jenny. He was one of the folks who saw her apparent resurrection at the end of the episode.

Felicity Jones as Robina Redmond in "The Unicorn and the Wasp"

Long before she gained nerd immortality as the ill-fated Jyn Erso in Rogue One: A Star Wars Story, the BAFTA-winning actress Felicity Jones appeared as an East End con artist in the-episode-where-the-Doctor-meets-Agatha-Christie.

Josh Dallas as Node 2 in "Silence in the Library"

You might be thinking, "Hey, I don't remember Josh Dallas in this episode!" Well, that's the reason this gallery exists. Also, it's because the man who would be Prince Charming on Once Upon a Time was one of the faces on the nodes in the iconic episode that introduced the world to River Song (Alex Kingston).

Colin Morgan as Jethro Cane in "Midnight"

As Jethro, a pre-Merlin Colin Morgan got stuck on a tour bus with the Tenth Doctor when a mysterious entity began attacking passengers and sowing the usual unsettling unrest that this series loves to bathe itself in. Although Jethro eventually tried to help the gang toss the Doctor on his arse, the Tenth Doctor remarked that Jethro was smart and he liked him.

Richard Dawkins as Himself in "The Stolen Earth"

The British scientist appeared on an in-universe television program to explain the phenomenon of the Earth being towed into the Medusa Cascade by the Daleks.

David Morrissey as Jackson Lake in "The Next Doctor"

David Morrissey's portrayal of a man who adopts the Doctor's identity after accidentally zapping himself with a Cyberman memory stamp was both heartwarming and heartbreaking--the perfect chaser after Rose Tyler (Billie Piper) got sucked into another universe and completely propelled the Tenth Doctor into a wibbly-wobbly, timey-wimey nervous breakdown.

Daniel Kaluuya as Barclay in "Planet of the Dead"

Daniel Kaluuya (Get Out, Black Panther) has had quite a career since playing Barclay, a passenger on a bus that traveled through a wormhole in "Planet of the Dead," the first and only Doctor Who Easter special.

Gemma Chan as Mia Bennett in "The Waters of Mars"

Humans and Crazy Rich Asians star Gemma Chan appeared as a geologist saved by the Tenth Doctor in "The Waters of Mars," a pretty creeptastic hour that also served as one of David Tennant's final goodbye specials.

Timothy Dalton as Rassilon in "The End of Time"

007 does Doctor Who, reviving a character with quite a complicated history if you reference the original run of the series. Essentially, Rassilon is the Lord High President of Gallifrey, the Doctor's home planet, and the guy who basically invented Time Lords. He's also kind of a douche.

David Harewood as Joshua Naismith in "The End of Time"

Before he was the CIA Director on Homeland or the Martian Manhunter on Supergirl, David Harewood played a 1-percenter who used his wealth to buy a broken Immortality Gate that he wanted the Doctor's nemesis, the Master, to repair. It ended REALLY WELL FOR EVERYONE, of course.

Olivia Colman as Mother in "The Eleventh Hour"

A modest appearance for Olivia Colman, the woman who would be the preggo BAMF in The Night Manager and her majesty QE2 in The Crown. Colman appeared in Matt Smith's first full episode as the Doctor as a mom.

Sophie Okonedo as Elizabeth X in "The Beast Below"

Tony Award-winning actress Sophie Okonedo showed that even before The Crown was a thing, being a royal isn't all pomp and parties. Sometimes, being the sovereign of the British empire means enslaving a space whale and electrocuting its brain so it keeps navigating your nation-ship to safety and then wiping your own memory so you don't have to keep thinking about how horrific that is. Yikes.

Iain Glen as Octavian in "The Time of Angels"

Before he was Jorah Mormont on Game of Thrones, Iain Glen portrayed Octavian, a bishop who had River Song released from prison to deal with a Weeping Angel, of all things.

Helen McCrory as Rosanna Calvierri in "The Vampires of Venice"

Helen McCrory of Peaky Blinders and Harry Potter fame appeared in this Eleventh Doctor adventure as the leader of a pack of aquatic vampire aliens who sought refuge from the Silence in 14th century Venice.

Toby Jones as Dream Lord in "Amy's Choice"

"Amy's Choice" is one of those delightful episodes that really delves into the fact that, for all of his delightful whimsy, the Doctor is a millennia-old survivor of horrific interdimensional war and, well, he's got some inner demons that therapy can't even touch. Toby Jones, of Dobby the House Elf and Captain America fame, portrays the Dream Lord, a dark manifestation of the Doctor who controls dreams and creates cruel scenarios to force the Doctor, Amy, and Rory to question their reality.

Bill Nighy as Dr. Black in "Vincent and the Doctor"

Bill Nighy had a small role as an uncredited curator who, unbeknownst to him, gave a tour of a Van Gogh exhibit to Vincent Van Gogh himself at the end of this beloved Eleventh Doctor outing.

James Corden as Craig Owens in "The Lodger"

Before he was singing carpool karaoke with the cute Beatle, James Corden shacked up with the Doctor when the TARDIS dumped Eleven in Colchester. The ultimate sad schlub, Corden's Craig got to be the hero and get the girl -- with a little intergalactic timey-wimey help, of course. He later reprised the role in an episode that revealed the Doctor could speak baby and that Craig's new child preferred to be called Stormageddon, Dark Lord of All.

Michael Gambon as Kazran/Elliot Sardick in "A Christmas Carol"

Doctor Who has a long and storied history of pilfering Harry Potter for talent. The 2010 Christmas Special, "A Christmas Carol," saw Dumbledore himself (well, the second Dumbledore) portray an Ebenezer Scrooge stand-in who Matt Smith's Doctor decides to torment in the name of holiday spirit and all that.

Mark Sheppard as Canton Everett Delaware III in "The Impossible Astronaut"

Is there a sci-fi or fantasy series out there that Mark Sheppard hasn't had a role in?

Hugh Bonneville as Captain Henry Avery in "The Curse of the Black Spot"

Oh look, another Downton alum. Lord Grantham himself set sail looking for some pirate booty and instead found himself on the wrong end of a curse in this early Eleven adventure.

Michael Sheen as House in "The Doctor's Wife"

Like Sir Ian McKellen and Imelda Staunton, Michael Sheen has also lent his voice to Doctor Who. In the beloved Season 6 episode "The Doctor's Wife," he brought to life House, a malevolent entity that fed on the TARDIS' energy.

Imelda Staunton as The Interface in "The Girl Who Waited"

C'mon, Doctor Who, we can do better than a voice role for the woman who portrayed the forever-awful Dolores Umbridge. As "The Interface," Staunton provided the voice for a planetary amusement park's guest services AI.

David Bradley as Solomon in "Dinosaurs on a Spaceship"

Another Harry Potter alum, David Bradley has popped up quite often in the Doctor Who universe. Most recently he appeared as the First Doctor in Peter Capaldi's final Christmas special "Twice Upon a Time," but he made an earlier onscreen appearance in Season 7 as Solomon, a pirate and murderer.

Sir Ian McKellen as the Great Intelligence in "The Snowmen"

Yes, that Ian McKellen. One of a handful of real life knighted actors to lend their talents to Doctor Who, McKellen lent his voice to the Great Intelligence, a non-corporeal being who thought non-melting snowmen were the ticket to world domination.

Tobias Menzies as Lieutenant Stepashin in "Cold War"

TV's good luck charm, Tobias Menzies was one of three familiar faces in the Season 7 episode "Cold War," which found Matt Smith's Doctor encountering an Ice Warrior on a Soviet submarine near the North Pole in 1983. Menzies played the ship's executive officer who had a bit of trouble believing in aliens.

James Norton as Onegin in "Cold War"

Grantchester's resident hunk James Norton also appeared in the episode "Cold War." He portrayed Onegin, a soldier who was killed by the Ice Warrior. RIP, Hunky Soldier. We hardly knew ye.

Liam Cunningham as Captain Zhukov in "Cold War"

Liam Cunningham is probably best known to many TV fans as Davos Seaworth on HBO's Game of Thrones (Doctor Who loves pilfering the Thrones cast as much as it loves its Harry Potter alums), but on Doctor Who he played the captain of Soviet submarine.

Dame Diana Rigg as Mrs. Gillyflower in "The Crimson Horror"

As the leader of a utopian doomsday cult, Dame Diana Rigg's Mrs. Gillyflower plotted to slaughter everyone on Earth... except for the perfect few she preserved. Of course, who was perfect and who wasn't was entirely based on her own opinion.

Warwick Davis as Porridge in "Nightmare in Silver"

Sci-fi and fantasy rockstar Warwick Davis fought the forever-upgrading Cybermen in this Neil Gaiman-penned episode during Season 7. Those people who say it's possible to have too much of a good thing are wrong.

John Hurt as the War Doctor in "The Name of the Doctor"

The Tinker Tailor Soldier Spy star embodied the infamous War Doctor, the persona adopted between Paul McGann's Eighth Doctor and Christopher Eccleston's Ninth Doctor during the 50th anniversary special. His was the darkest incarnation of the Doctor, a pragmatic, but conflicted character tasked with doing the most dreadful deeds of the Time War between the Daleks and the Time Lords.

Foxes as Singer in "Mummy on the Orient Express"

The Grammy-winning musician brought her talent to the Who-niverse with a jazz cover of the Queen hit "Don't Stop Me Now." God, this show is so British.

Nick Frost as Santa Claus in "Last Christmas"

Nick Frost, aka Simon Pegg's bestie in pretty much all of the Three Flavours Cornetto films, completed the set almost a decade after Pegg's appearance in the Who-niverse. He appeared in the TK Christmas special as a Santa who, in tried and true Doctor Who fashion, isn't actually Santa Claus. Sort of. It's complicated.

Paul Kaye as Albar Prentis in "Under the Lake"

You might not have recognized Paul Kaye, but he portrayed an undertaker who later returned as a ghost in the two-parter "Under the Lake" and "Before the Flood."

Maisie Williams as Ashildr in "The Girl Who Died"

Best known as Arya Stark in Game of Thrones, Maisie Williams also appeared for a run of episodes as the Viking-turned-immortal-adventurer Ashildr. She is currently flying a TARDIS that looks like a 1950s diner with former companion Clara Oswald (Jenna Coleman), and we like to think we'll run into the pair in the future. Or past. Future past? You know how it is.

Letitia Wright as Anahson in "Face the Raven"

Letitia Wright is now best known for playing Shuri in the Marvel films Black Panther and Avengers: Infinity War. But before she was making fun of T'Challa's footwear and fixing white boys, she was Anahson, a young girl disguised as a boy in order to hide her from anyone who might want to take advantage of her ability to see into the past.