Australian actor Christopher Chung joins the cast of Doctor Who Season Two as a character simply known as ‘Cassio’ and ‘Trooper One’. He will meet the Doctor (Ncuti Gatwa) and new companion Belinda Chandra (Varada Sethu) for a thrilling adventure in the forthcoming second season – described by showrunner Russell T Davies as one of the “toughest episodes we’ve ever made”.

I’ve been aware of Chung’s casting since another Doctor Who Season Two actor mentioned him on social media and I took a screenshot of his CV on 1 March 2024. He was filming during Block 3, directed by Amanda Brotchie. Block 3 is believed to consist of Episode Two written by Russell T Davies and Episode Three written by Sharma Walfall and Russell T Davies.

In the newly-released publicity image, Cassio appears to be wearing a similar underwater suit as shown in this scene from the Doctor Who Season Two teaser trailer. This makes it likely that Chung is in Episode Three, rumoured to be titled Five Miles Deep.

On the casting, Doctor Who showrunner Russell T Davies said:

“I’m a huge fan of Slow Horses, and I was so excited to get Chris involved. He brings all of his strength and style and talent to one of the darkest, toughest episodes we’ve ever made. As for whether Cassio is an ally or an enemy of the Doctor, you’ll have to wait and see, but I can promise, it’s one hell of a meeting!”

Davies refers to Chung’s roll as the tech-savvy MI5 agent Roddy Ho in the Apple TV+ drama Slow Horses. Chung also starred in BBC’s Waterloo Road, and the Steve McQueen 2024 movie, Blitz.

Davies also had this to say about Cassio on Instagram:

“’Nuke the place from orbit.’ SO HAPPY to get Chris on board! He’s playing a tough Trooper who finds himself… ah, well, you’ll find out. But this one’s brutal, good luck Trooper One!”

Christopher Chung said:

“I’m absolutely thrilled to step into the Whoniverse as Cassio for Season 2! This show is legendary, and getting to be part of this new era feels surreal. Working with Russell and Ncuti has been a dream! This episode is huge – packed with everything Who fans love: heart, adventure, and a touch of madness. I can’t wait for everyone to see what’s in store—it’s going to be iconic. Get ready!”

Doctor Who Season Two, starring Ncuti Gatwa, Millie Gibson and Varda Sethu, will transmit in April and May 2025 on BBC One, BBC iPlayer and Disney+ where available.