The Pelosians were the natives of Pelos. They were humanoid with a pair of small horns jutting from each temple and eyebrows that stretched out to merge with their hairlines. Their skin tones ranged from light auburn to rich maroon. The horns varied in size and sharpness, depending on race. They worshipped gods which they called Originators.
When the USS Enterprise discovered their world in November 2270, the Pelosians were suffering intensely from famine, radiation and plague caused by an interstellar dust cloud blocking their sun. The collapse of governments across Pelos allowed the strongest nation, ruled by Queen Palchelle, to conquer what was left. She claimed that the gods had inflicted the disasters upon them, and forbade the practice of medicine on the grounds that only the gods should determine who lived or died. With Spock and McCoy predicting that the Pelosians would be wiped out within two years, Captain Kirk secretly gave assistance to the rebellion which overthrew the empress, gave them McCoy's cure for the plague, and used the ship's deflector dish to thin out the dust cloud, all without revealing the existence of other worlds.
However, Kirk's actions on Pelos were observed by Commodore Harriet Griswold, who charged him with violating the Prime Directive and ordered the ship back to Earth. (TOS novel: Ex Machina, DTI novel: Forgotten History)