Troglytes were the manual labor class in the society of planet Ardana. Troglytes were largely restricted to the surface of the planet, with any travel to and within the Cloud City of Stratos being closely regulated and monitored.
Troglytes were considered by the Ardanan Stratos City Dwellers to be an intellectually and emotionally inferior race. In fact, a gas generated by the zenite mined on Ardana had a deleterious effect on the thought processes of the surface dwellers (as well as other humanoid species). In 2269, the United Federation of Planets provided the Troglytes with air filtering technology which enabled them to counteract and reverse the damage done by this gas. (TOS episode: "The Cloud Minders")
However, the social divisions and unequal treatment by the upper class City Dwellers continued, eventually leading in the late 23rd century to a civil war, known as the Great Disruption. Following this war, Stratos was abandoned and the class distinction was largely eliminated; however, some Troglyte descendants in the late 24th century considered the continued existence of Stratos to be an unwanted reminder of the inequalities of the past. (CoE eBook: Signs from Heaven)