While the Doctor and their regular companions are always the stars of the show on Doctor Who, most episodes feature one-off characters that play major roles in the plot of the story of the week. Sometimes, these characters might pop up once or twice more, recurring throughout a season and connecting to that season's overarching plot. Though their tenures may be brief, that hasn't stopped some from becoming fan favorites.

Since Doctor Who has been on the air for almost sixty years, it's no surprise that a vast number of actors — including some recognizable faces — have lent their talents to this classic sci-fi show. While guest roles are a great way to showcase unsung talent in the acting world, there are also many beloved actors who haven't yet made appearances on the program. Any of these guest stars could create huge interest for a big episode — and make for a great watch.

7 Nathan Fillion

Nathan Fillion as Malcolm Reynolds & Richard Castle

A beloved name in the world of television, the star of Firefly and Castle would make a wonderfully unexpected, yet completely fitting, guest appearance on Doctor Who. With his acting chops and his talent for quips, sci-fi fans are never disappointed when Nathan Fillion graces screens.

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Fillion could play any number of roles in a Doctor Who guest appearances, but audiences would jump for joy to see him return as an outer-space scavenger or an outlaw on a futuristic world, hearkening back to his roots as Malcolm Reynolds. His character might use his rakish charm to deceive the Doctor and friends, or he might become a reluctant ally, throwing out one-liners to keep the mood light.

6 Phoebe Waller-Bridge

Fleabag talking to the camera while pointing at her family, including Sian Clifford as Claire

The brilliant mind behind shows like Fleabag and Killing Eve has shown her onscreen talent as the lead character in the former. Waller-Bridge has a snarky, distinctly British sense of humor that would undoubtedly translate well into Doctor Who, and it's easy to imagine her tagging along with the Doctor and friends for an episode or two.

Waller-Bridge could play any number of guest roles, from a clueless civilian who falls into an enemy trap, to a hardheaded skeptic who refuses to believe that an alien invasion is occurring. Regardless, her excellent comic timing would be a perfect fit for a lighthearted escapade, one in which the Doctor inevitably saves the day.

5 Kyle McLaughlin

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From Twin Peaks to David Lynch's Dune, McLaughlin is no stranger to roles that allow him to explore the supernatural or the science fictional. Many of his characters are quirky or unique, the perfect fit for a show like Doctor Who. Though non-British actors don't appear on the show very often, McLaughlin's acting skill and his talent for deadpan comedy would fit in well with the show's distinctive feel.

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If McLaughlin were to appear on the show (which is, admittedly, unlikely), he could make a callback to his days as Special Agent Dale Cooper on Twin Peaks, perhaps appearing as a member of an American version of UNIT. He has also demonstrated a talent for portraying a sinister presence (as in the Twin Peaks revival), and may make a fantastic villain in Doctor Who as well.

4 Nicola Coughlan

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Surprisingly few Irish actors have been featured on Doctor Who, and as a rising star of the past few years, Nicola Coughlan has great potential to represent Ireland in the iconic sci-fi program. Thanks to her roles as Claire Devlin on Derry Girls and Penelope Featherington on Bridgerton, Coughlan has shown that she can fit into roles in a wide variety of eras — and a guest role on Doctor Who could take her anywhere in space and time.

Both of her best-known roles show Coughlin playing characters of great intelligence and wit. She could to a researcher whose intellect keeps the Doctor on his toes, or a so-called conspiracy theorist whose predictions of alien invasion turn out to be right.

3 Peter Dinklage

Tyrion Lannister in Game of Thrones season 7

Most know him now for his role as Tyrion Lannister on Game of Thrones, but Peter Dinklage has had a long and storied acting career. An immensely talented performer who refuses to be typecast by appearance, Dinklage would bring great star power to Doctor Who.

Having played heroes, villains, and everything in between, Dinklage could appear in any number of Doctor Who side character archetypes. Perhaps he could appear as a sinister-seeming character who turns out to be more friend than foe, or a heroic figure who sacrifices himself in a moving moment to stop the monster of the week.

2 Maggie Smith

Maggie Smith as Professor Minerva McGonagall in Harry Potter

Hailing from Britain and having such a long and illustrious acting career, it's surprising that Maggie Smith hasn't appeared on Doctor Who before. Being such a recognizable face and name, if she does appear on the sci-fi show, it would be fitting to see her represent a well-known historical figure.

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It's been some time since Doctor Who viewers got a solid historical episode. Smith would be an excellent addition to such a story, especially considering her history of acting in period pieces. An actor as talented as Smith could portray anyone from Queen Elizabeth I to Marie Curie, giving the show an opportunity to spotlight some amazing women from history.

1 John Noble

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Perhaps most famous nowadays for his role as Walter Bishop on Fringe, Noble has more than proven his talent for taking on the role of mad scientist or eccentric genius. Considering that most incarnations of the Doctor bear this same quality to some degree, it would be interesting and entertaining to watch two such characters connect onscreen.

With Noble's talent and emotional intensity, he could fit into a number of single-episode roles. Perhaps his character would appear to be friendly and innocuous at first, but is secretly a manipulative villain luring the Doctor and their friends into a trap. On the other hand, he might portray a brilliant but troubled individual much like his character on Fringe, who inadvertently causes a catastrophe that the Doctor must resolve.

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