The Uxarieans created and tested the Doomsday Weapon, but never used it. Their culture began to decline, turning away from scientific achievement and entering into a kind of Dark Age. They evolved into three different species: the so-called Primitives, who had three fingers on each hand, striped green skin and carried long spears; the Priests, who had pale skin and large, ridged heads, and were nearly blind; and the small, pale Guardian who ruled over the underground city, who had advanced powers including the ability to teleport objects. The Primitives had rudimentary telepathic ability, being able to understand what aliens were saying even if they did not understand the language.
Some time before 2471, human colonists first came to Uxarieus. Two of them were killed for trying to enter the city, but a truce was reached and the Primitives began working as assistants to the humans in exchange for food. A year later, the Master came to Uxarieus in search of the Doomsday Weapon, posing as an Adjudicator. The Third Doctor convinced the Guardian that he should not have it, and it was set to self-destruct. (TV: Colony in Space)