Ross Brimmicombe-Wood

Ross Brimmicombe-Wood was a career soldier and heavy nationalist. In his early army career, he had been friends with Charles Crichton and Robert Dalton, both of whom would end up as UNIT-UK commanding officers. (Project Valhalla)

Years later, as a Colonel, he was the commanding officer of the UK branch of UNIT. He was believed to be abducted while escorting alien cargo across the country.(BFA: Time Heals)

However, in reality he was the Commanding Officer and a double-agent for the ICIS; he had faked his own kidnapping in order to create chaos in UNIT. He was involved in attempts to bring down the government for reasons of ultra-nationalism, and was imprisoned for his actions. (BFA: The Wasting)

Alternate universe
In an alternate universe, Colonel Brimmicombe-Wood was the leader of UNIT, following a disgraced Brigadier Alistair Gordon Lethbridge-Stewart. He lead a team to Hong Kong to retrieve Ke Le. (DWU: Sympathy for the Devil)