D is for... Dominators

A sadistic war-like race of humanoids, who claimed to be the Masters of the Ten Galaxies. One of their ships, commanded by Navigator Rago, was sent to the planet Dulkis to determine its usefulness as a source of slave labour. Their vessels were fueled by absorbing local radiation, so they landed on an island that had once been the site of a nuclear bomb test. Accompanying Rago was a Probationer named Toba. He was even more sadistic and hot-headed than his superior, who preferred a more methodical approach. The two quarreled repeatedly, and Rago had to pull rank on his Probationer on several occasions to ensure he concentrated on their mission. The Dominators employed squat robots called Quarks as both weapon and workforce. Rago had to remind his colleague that their power supplies were low and the robots had to be conserved in order to carry out their mission.
When it became clear that the Dulcians would not make good slave workers, Rago was given a new mission - to turn the planet into a nuclear mass suitable for the refueling of the Dominator fleet.
The Doctor was able to intercept the atomic seed capsule which was intended to achieve this and hid it aboard their spaceship just as it took off. Rago and Toba were killed in the explosion.

Played by: Ronald Allen (Rago) and Kenneth Ives (Toba). Appearances: The Dominators (1968).