The alien ambassador's species were peaceful, advanced, radiation-dependent humanoids who emitted deadly levels of radiation and could channel blasts of energy from their hands. Completely alien in many ways, they communicated via radio communication impulses rather than speech and were not susceptible to G-force. They were also impervious to bullets due to some kind of force field.
The species used enormous, half-mile wide, discoid-shaped spacecraft and could create different environments inside. They also possessed mind conditioning technology and weapons capable of destroying worlds.
Three alien ambassadors visited Earth some time after making contact with a human exploration mission on Mars, where one astronaut named Jim Daniels was accidentally killed because the ambassadors had no way of knowing their touch was fatal to humans. Carrington, the surviving astronaut from that mission, by then a high-ranking British army officer, kidnapped the ambassadors. After forcing them to carry out a series of raids and murders, his organisation planned to expose their existence to the world, stirring up public opinion and forcing world governments to launch a nuclear strike against their spacecraft. This plan was defeated by the Third Doctor and the ambassadors were returned. (TV: The Ambassadors of Death)