Cheron is a planet that supported a flourishing civilization around 48,000 B.C.E. (TNG novel: The Buried Age) It supported a race of humanoid natives who had curious skin coloring, divided perfectly along the middle: Some were black on the left side and white on the right, others were white on the left side and black on the right. Several millenia ago, both sides completely wiped each other out in a series of wars based on mutual racial hatred. (TOS episode "Let That Be Your Last Battlefield")
Cheron was also located in a strategic position relative to the planet Vulcan. Some time before the 22nd century, the Romulan government occupied the planet and began to use it to spy on their ancient cousins. (ENT novel "Kobayashi Maru") The planet would later become the location of the Battle of Cheron, a humiliating defeat for the Romulan government during the Earth-Romulan War.