The Ardanans were humanoid natives of the planet Ardana, a member of the United Federation of Planets. Ardanans were very famous for their anti-gravitational city, named Stratos, which floated in the sky. They were also known for their export of zenite. (TOS: "The Cloud Minders")
City-dwellers ruled the planet from Stratos through a council existing solely of their class, justifying the total suppression of the Troglytes based on the widely held belief that as an inferior species the Troglytes were incapable of advanced culture like there existed on Stratos. As of 2269, Plasus held the position of high advisor of the council.
Troglytes on the other hand were considered to be mentally inferior, and therefore performed all the physical toil necessary to maintain Stratos, most notably mining Zenite. Unknown to both city-dwellers and Troglytes however, this mental disadvantage, while real, was only the result of exposure to a gas emanating from unrefined zenite, and furthermore, fully reversible.
Troglytes felt suppressed and wanted access to Stratos, and at some point a resistance group known as the Disrupters was formed, mainly under the impulse of Troglytes that had been away from exposure to the gas due to duties in Stratos. They tried to put pressure on the city-dwellers by withholding zenite and capturing hostages. When the USS Enterprise visited Ardana in 2269, they had been active for several months. Due to intervening by the crew of the Enterprise, this situation was exposed to Starfleet, and apart from a direct suggestion to start using breathing masks in mining so that the Troglytes could recover their full mental capacities, the people of Ardana were referred to the Federation Bureau of Industrialization to resolve their differences. (TOS: "The Cloud Minders")