O (Spyfall)

"O" was a member of the British Secret Service agency, MI6. According to the Thirteenth Doctor, he was one of their best. O had previously been a champion sprinter, something which was noted in his official file.

According to a man who claimed he was, O was abducted at the start of his new career, and miniaturised using a Tissue Compression Eliminator. The man kept what appeared to be the original O in a matchbox. He showed this to the Thirteenth Doctor to support his story. (TV: Spyfall)