Varada Sethu’s Doctor Who Debut Continues a Classic Doctor Who Tradition

•  “Boom” marks the return of Steven Moffat to Doctor Who, with nods to previous episodes and a surprise debut of Varada Sethu.
•  Varada Sethu’s dual roles on Doctor Who mirror past instances of actors returning as major characters in subsequent seasons.
•  Sethu’s appearance as Mundy Flynn may hint at a “timey-wimey” storyline similar to Jenna Coleman’s Clara Oswald in the series.

“Boom” is the third episode of Doctor Who Season 1 that welcomed veteran Doctor Who writer Steven Moffat back to the sci-fi series. The episode took the Doctor into new territory, but also revisited some familiar ground for the show. There were more than a few nods to Moffat’s previous work on the series, with the return of the Anglican Marines (a reference to when the Doctor stole the moon and the President’s wife), and a mention of fish fingers and custard. However, another trend from Doctor Who history also got a surprise revival when Varada Sethu appeared as Mundy Flynn. The actor was originally announced to be playing a new companion in Doctor Who Season 2 in 2025.

Mundy Flynn was one of the Anglican Marines waging war on the world of Kastarion 3 in “Boom,” though showrunner Russell T Davies has confirmed Varada Sethu will be playing a different role when she returns in 2025. This continues a trend in Doctor Who to recast guest stars as major characters in subsequent seasons. Since Doctor Who‘s 2005 revival, three companions have been played by actors who had already appeared on the show in separate roles. Two of the Doctors even took on the role after previously appearing as other characters. Throughout the classic and modern series of Doctor Who, many more actors have appeared in two or more roles — a distinction Varada Sethu is also about to gain.

Varada Sethu’s Two Roles on Doctor Who, Explained

In April, it was announced that Varada Sethu would be stepping into the TARDIS alongside Ncuti Gatwa and Millie Gibson as a new companion in Doctor Who Season 2. The announcement followed speculation from fans that Sethu would be replacing Gibson as the series’ main companion when she was spotted shooting scenes for the show on location without Gibson present. The official casting announcement confirmed that Sethu was joining the second season as a new companion, but dispelled rumors she would be replacing Gibson’s Ruby Sunday or relegating Ruby to a guest role. The name of Sethu’s Season 2 character has not yet been revealed, nor have any details of her backstory.

Following this announcement, Doctor Who fans were surprised to see Varada Sethu make her debut on the series a whole season early, in Episode 3 of Season 1, “Boom.” The episode saw the Doctor and Ruby arriving at the war-torn world of Kastarion 3, where the Anglican Marines last seen during Steven Moffat’s era as Doctor Who showrunner had declared war on the Kastarions. When the Doctor stood on a landmine, leaving him unable to move without setting it off, Sethu’s Mundy Flynn soon found him on the battlefield. Realizing the Doctor’s Time Lord biology would trigger an explosion large enough to destroy half the planet, Mundy tried to help him prevent the mine from activating.

Since Sethu’s appearance in the episode, Russell T Davies has confirmed via Instagram that she will not be playing Mundy Flynn again in Doctor Who Season 2. Instead, she will return as a brand-new character, though it seems likely her characters’ resemblance will not be ignored and will factor into the second season’s plot. Davies’ Instagram post teases that “things are about to get timey-wimey” and that “quite how Varada returns will be revealed next year.” The video commentary for “Boom,” available on BBC iPlayer, also reveals that the episode’s writer, Steven Moffat, was not aware of Sethu’s return as the Doctor’s new companion. It’s therefore not clear whether Mundy Flynn was always part of a larger plan from Davies, or whether Sethu simply impressed the producers enough to be invited back for a bigger role.

Sethu’s appearance as Mundy Flynn ahead of her stint as a companion is far from the first time an actor in a one-off guest role has returned to Doctor Who as the Doctor’s companion. Davies’ tease of a “timey-wimey” story dealing with Sethu’s return as a different character suggests her Doctor Who journey will resemble that of Jenna Coleman’s Clara Oswald. As a companion of Matt Smith’s Eleventh Doctor, Clara joined the Doctor following the departure of Amy Pond and Rory Williams. Before the Doctor met Clara, however, he met two of her doppelgängers — a starship entertainment manager called Oswin Oswald and a Victorian barmaid/nanny, Clara Oswin Oswald. These were later revealed to be splinters of Clara, formed when she entered the Doctor’s time stream.

Other Companions and Doctors who Previously Appeared on Doctor Who

Played by Freema Agyeman, Martha Jones was the Tenth Doctor’s second companion, meeting him shortly after he was separated from Rose Tyler. Agyeman first played Martha in the first episode of Doctor Who Series 3, “Smith and Jones.” This saw the Doctor posing as a patient at the hospital where Martha was studying, tracking down a Plasmavore that also caught the attention of the Judoon. However, before Martha made her Doctor Who debut, Agyeman appeared in the Series 2 finale as Torchwood employee Adeola Oshodi. In “Smith and Jones,” Martha revealed that Adeola was her cousin, referencing her death as seen in “Army of Ghosts.”

2008’s “The Fires of Pompeii” is noteworthy for featuring two actors who would go on to play leading roles on Doctor Who, in Karen Gillan and Peter Capaldi. Gillan appeared as a Soothsayer in “The Fires of Pompeii,” serving the sinister Pyroviles, who were planning to use Mount Vesuvius to devastate the Earth. Gillan would return in Series 5 as the Eleventh Doctor’s first companion, Amy Pond. Meanwhile, Capaldi played by the Roman marble trader, Lobus Caecilius, the man whose family the Doctor saved from Vesuvius’ eruption. When Capaldi later returned to Doctor Who as the Twelfth Doctor, he acknowledged the familiarity of his new face and later remembered that he had taken the face from Caecilius — a reminder of his duty to save people.

Actors being recast in this way is not unique to the modern series of Doctor Who. The classic series saw several actors appearing in multiple roles, though none were quite as prolific as Colin Baker. Best known for playing the Sixth Doctor from 1984 to 1986, Baker first appeared on Doctor Who opposite his predecessor, Peter Davison. In 1983’s “Arc of Infinity,” Baker portrayed Commander Maxil, another Time Lord and commander of the Gallifreyan Chancellery Guard. Maxil was antagonistic towards the Doctor and the reason the Sixth Doctor adopted his appearance was never revealed on the show. By contrast, when Lalla Ward took over from Mary Tamm as the Fourth Doctor’s Time Lord companion, Romana, she openly acknowledged she had taken her new appearance from Princess Astra, Ward’s previous Doctor Who role.

Doctor Who’s Other Notable Recasting Choices

Outside of these Doctors and companions, a handful of other actors appearing in the Whoniverse have been recast in larger roles across Doctor Who and its spinoffs. One of the best known ones is Eve Myles, who initially appeared on Doctor Who before going on to play one of the leads on the adult spinoff, Torchwood. On Doctor Who, Myles appeared opposite the Ninth Doctor, Christopher Eccleston, in 2005’s “The Unquiet Dead.” She played the psychic servant Gwyneth, who gave her life to protect Earth from the ghostly Gelth. Myles was then recast as Torchwood’s new recruit, Gwen Cooper, on the spinoff series. In a crossover appearance on Doctor Who, the Tenth Doctor and Rose Tyler noticed Gwen’s resemblance to Gwyneth and deduced the two were related.

The Sarah Jane Adventures (a Doctor Who spinoff aimed at younger viewers) also saw the casting of two actors who would go on to play roles alongside the Thirteenth Doctor, Jodie Whittaker. Bradley Walsh first joined the Whoniverse on The Sarah Jane Adventures in the Season 2 story, “The Day of the Clown,” in which he played the Pied Piper. Walsh would later accompany the Thirteenth Doctor in the TARDIS as companion Graham O’Brien. Meanwhile, Anjli Mohindra was a series regular on The Sarah Jane Adventures, playing Sarah Jane Smith’s friend Rani Chandra, who went on to play the spider-like Queen of the Skithra on Doctor Who, in the 2020 episode, “Nikola Tesla’s Night of Terror.”

Only time will tell whether Varada Sethu’s Doctor Who debut as Mundy Flynn will be significant to her new companion character, or whether the two roles will be treated as broadly separate. However, after her first appearance in “Boom,” fans seem sure to respond warmly to Sethu’s full-time role on the TARDIS. While viewers are hoping to soon find out the meaning behind the much more blatantly purposeful recasting of Susan Twist in several Doctor Who Season 1 episodes, they will have to wait a little longer to discover the truth about Varada Sethu’s return.