After operatives both for MI6 and all other spy organisations on Earth were attacked by the Kasaavin, "C" sent operatives to retrieve the Thirteenth Doctor, Ryan Sinclair, Yasmin Khan and Graham O'Brien. He briefed the group on the attacks and asked them to investigate, believing alien technology was involved. Whilst presenting them with spy-gadgets, "C" was shot dead by the Spy Master, using a Mandraffian laser rifle. His last word was a befuddled "……Oh", hinting at the identity of his killer. (TV: Spyfall)
Behind the scenes
Prior to taking on the role of "C" in the Doctor Who universe, actor and comedian Stephen Fry had portrayed a head of the British secret services always referred to as "Control" in a notorious series of sketches from the anthology comedy series A Bit of Fry and Laurie.
In parallel to the joke inherent in the casting of "C", the character of a portly head of British secret services whose code name is a single letter is reminiscent of "M", head of MI6 in the James Bond franchise. "C", however, is also traditional shorthand used to refer to the head of MI6 in the real world.