The Battle of Cheron in the history of Star Trek is the victory of pre-Federation Earth forces over the Romulan Star Empire. Little is known now about its circumstances, but Earth's victory indirectly led to the formation of the United Federation of Planets and cut off all contact with the Romulans for just over a century.

Even by 2366, the Battle of Cheron had not been forgotten by the Romulans (from the Star Trek: The Next Generation episode "The Defector").

It is interesting to note that the "half-black, half-white" aliens of TOS "Let That Be Your Last Battlefield", Bele and the rebel Loki, were from the planet Cheron.

Any connection between these two Cherons has yet to be revealed.

However, Bele and Loki's Cheron had been depopulated by a horrific civil war at least several hundred years before the Romulan War, the two rival factions on the planet driving their race to extinction.