Douglas Jardine was an English cricketer who was in Australia in 1933, having been involved in a test match against the national side. He had met Flora and had travelled with her and her mother.
When he and his friends encountered the Doctor, Douglas started to show unusual symptoms, mainly (in one instance) having the voice of a Dalek. The Doctor eventually realised that he was not the real Douglas Jardine.
He, Flora and Mrs Calderwood vanished shortly after the Doctor's arrival. (AUDIO: Aimed at the Body)
The Doctor would eventually discover that Douglas, along with many other people throughout history who looked like him, were caused by a group of Time War Daleks who — while on a mission to prevent the rise of Time Lord society on Gallifrey — created a time distortion which created alternate versions of themselves as four un-mutated Kaled people. This time distortion also caused there to be multiple copies of these four Kaleds to appear at various points throughout time and space. (AUDIO: Effect and Cause)