Space captain

An alien space captain was in charge of the attempt by a group of radioactive aliens to make peaceful contact with Earth during the 1970s.

Biography
The Third Doctor was brought aboard the alien captain's ship after travelling into space in Recovery 7 in search of three missing astronauts. The captain directed him to where the three astronauts — Van Lyden, Michaels and Lefee — were being kept, conditioned to believe they were in Space Control's quarantine area back on Earth.

The captain then spoke to the Doctor — using a translation machine — over a large video screen, wanting to know why their ambassadors had not been returned. The Doctor insisted the Earth authorities knew nothing of the arrangement and persuaded the captain to let him return to Earth, although the captain insisted on keeping the three astronauts until the ambassadors were returned.

The captain later contacted Space Control via video link, warning that the aliens had the power to destroy Earth and would use it unless their ambassadors were returned. (TV: The Ambassadors of Death)