Meet the cast of Doctor Who – Boom

The new episode sees the Doctor (Ncuti Gatwa) and Ruby Sunday (Millie Gibson) arrive on Kastarion 3, a bleak and war-torn planet. The Doctor accidentally steps on a landmine, and has to somehow figure out a way to save himself, Ruby, and an entire planet without moving.

Plus, we've just been introduced to companion we weren't meant to meet for another year, as Varada Sethu officially joins the cast!

Basically, we've got a classic Moffat adventure to delve into – tense, gripping, and just a little bit unhinged.

So, as Boom arrives, here's everything you need to know about that glorious cast.

Doctor Who – Boom cast: Full list of actors and characters

The actors and characters in Doctor Who's new episode, Boom, are:

• Ncuti Gatwa as the Doctor
• Millie Gibson as Ruby Sunday
• Varada Sethu as Mundy Flynn
• Joe Anderson as John Francis Vater
• Majid Mehdizadeh-Valoujerdy as Carson
• Caoilinn Springall as Splice Alison Vater
• Bhav Joshi as Canterbury James Olliphant
• Susan Twist as Ambulance

Of course, more roles could be revealed in the episode, but fans will have to watch to find out.

Ncuti Gatwa plays the Doctor

Who is the Doctor? The Doctor is a time traveller from Gallifrey. Currently, he's travelling the universe with companion Ruby and, in Boom, we get to see a new side to him as he faces catastrophic consequences if he even moves a muscle.

Where have I seen Ncuti Gatwa before? Before being cast as the Fifteenth Doctor, Gatwa made his name as fan favourite Eric Effiong in Sex Education. He's also graced the big screen, most prominently alongside Ryan Gosling in Barbie, and also starred in Apple TV+'s Masters of the Air.

Millie Gibson plays Ruby Sunday

Who is Ruby Sunday? Ruby is the Doctor's newest companion, with Boom marking her first time on an alien planet. It's likely that, with the Doctor pretty much out of action, we'll see her step up. Plus, she's still got a major mystery to contend with – what on Earth are all the strange happenings that she seems to be causing?

Where have I seen Millie Gibson before? Before being cast in Doctor Who, Gibson was best known as Kelly Neelan in Coronation Street.

Varada Sethu as Mundy Flynn

Who is Mundy Flynn? Mundy Flynn is an Anglican Marine who has a close bond with Canterbury and Splice. She's initially apprehensive of the Doctor and Ruby but ultimately helps them.

Where have I seen Varada Sethu before? Sethu is no stranger to roles in big sci-fi franchises after her role as Cinta Kaz in Andor. She's also appeared in the series Annika and the film Jurassic Park: Dominion. In April 2024, it was confirmed that Sethu had been cast as a new companion for Doctor Who season 15 to form a TARDIS trio alongside Ncuti Gatwa and Millie Gibson.

Joe Anderson as John Francis Vater

Who is John Francis Vater? John Francis Vater is an Anglican Marine and the father of Splice. He has a key role to play in protecting his daughter.

Where have I seen Joe Anderson before? Anderson has had many roles across film and TV, with early roles being in Midsomer Murders and Afterlife. In 2007, he starred in the film Across the Universe as Max Carrigan. He's also appeared in The 27 Club, The Ruins, The Crazies, and The Grey as well as the last Twilight film, Breaking Dawn: Part 2. In 2015, he took over as Mason Verger in Hannibal, and his most recent role was as Laurentz in the film The Last Front.

Majid Mehdizadeh-Valoujerdy as Carson

Who is Carson? Carson is an Anglican Marine and a close friend of John Francis Vater's.

Where have I seen Majid Mehdizadeh-Valoujerdy before? Mehdizadeh-Valoujerdy, who has also been credited as Luke Jerdy in previous roles, is best known as Jesse Donovan in Hollyoaks, a role he held from 2016 to 2020.

Caoilinn Springall as Splice Alison Vater

Who is Splice Alison Vater? Splice the daughter of John Francis Vater, and a youngster who meets the Doctor and Ruby.

Showrunner Russell T Davies previously issued an ominous warning about the character, saying on the Official Doctor Who Podcast: "There's a great supporting cast and there's a great supporting character called Splice, and one thing I would say in this story is be very careful about saying Splice's father's name out loud."

Where have I seen Caoilinn Springall before? Springall has previously appeared in the 2020 film The Midnight Sky as Iris, the series Citadel as Hendrix Conroy, and the film Stopmotion.

Bhav Joshi as Canterbury James Olliphant

Who is Canterbury James Olliphant? Canterbury is an Anglican Marine and has a close bond with Varada Sethu's Mundy Flynn.

Where have I seen Bhav Joshi before? Joshi is known for roles including Anil in Wedding Season, DI Jay Mallic in Granite Harbour, and Anu Kapoor in The Diplomat. He's also appeared in Vigil, Deadwater Fell, and the Apple TV+ film Tetris.

Susan Twist as Ambulance

Who is Ambulance? Susan Twist plays an AI 'Ambulance' - an AI system that eliminates marines when they become too costly.

Where have I seen Susan Twist before? Fans will already have seen Twist in various Doctor Who episodes including Wild Blue Yonder, The Church on Ruby Road, Space Babies and The Devil's Chord. At present, the actress is appearing in every new episode in a different role, with various theories floating about regarding who she actually is. Could she be a foe to the Doctor, or potentially a friend? Only time will tell.

Aside from Doctor Who, Twist is known for appearing in shows including Coronation Street, The Archers, In The Flesh, and Doctors.

Doctor Who continues with Steven Moffat's Boom on 18th May on BBC iPlayer and BBC One.

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