The Ajacks were miners from Megropolis Three on Pluto. Since the PCM conditioning was not effective in the mines, the Ajacks were more independent than most workers under the control of the Company. Gatherer Hade described the Ajacks as "an arrogant, unsettled lot" and noted that conventional wisdom held that if there was ever to be a rebellion against the Company, it would start among the Ajacks.
Gatherer Hade, Marn and Mandrel all thought that the Fourth Doctor looked like an Ajack, so it would seem that Ajacks had more flamboyant dress senses than other workers on Pluto. (TV: The Sun Makers)