Frogmen were bipedal with oval heads and large orange eyes. They had three bulbous fingers on each hand. Their legs were powerful, allowing them to leap high in the air.
In the 2260s, frogmen invaded Muton, a class M planet in the star system adjacent to theirs. The frogmen murdered most of the Muton natives, retaining a large slave population in the capital city. They deployed rock creatures to keep watch for intruders near the city.
In 2265, a hover-saucer manned by four frogmen detected James T. Kirk and Spock on the surface. The Starfleet officers were nearly killed, but three of the patrol crew were dispatched by arrows fired from a group of Muton rebels. A fourth crewman escaped and radioed for reinforcements.
Spock helped repair the rebels' crashed patrol cruiser, and it was able to launch an assault on the capital city that drove the frogmen to open country. Rebel leader Dalbar freed the slaves and took control of various transport ships, intending to free his world from the invading frogmen. (TOS comic: "Slaves of the Frogmen")