Raldonn

Raldonn was an alien that crashed on late 20th century Earth. His spaceship was powered by psychic energy and required at least two beings to provide enough to run it. Raldonn's co-pilot was killed in the crash, so he was stranded.

The British government asked him to "help" them with technological research. He was put in charge of Operation Proteus, which he was secretly using to create a virus to mutate a human into his species, allowing him to finally leave the planet.

He released the virus in King's Cross station. Some of prior subjects went mad and killed him. The First Doctor created a genetic stabiliser to counteract the virus. (COMIC: Operation Proteus)