George Carrington

General Carrington was a British military officer and the head of the Space Security Department.

He had previously been an astronaut on Mars Probe 6, where an alien accidentally killed Jim Daniels, a member of his crew.

Afterwards, Carrington worked with Sir James Quinlan to capture three of the aliens and use them to start a war between Earth and the aliens. Carrington was eventually stopped thanks to the Third Doctor's efforts. (DW: The Ambassadors of Death)