The inhabitants of Solais V, whose factions had fought one another for fifteen centuries before asking the Federation for the deaf mediator Riva in Loud as a Whisper.
The Solari are the people of Solais V, seen in the Next Generation episode Loud as a Whisper. Their two factions have been at war for some fifteen hundred years, to the point where the population faces extinction and neither side remembers a time of peace.
In 2365 the Solari ask for Riva, a famous mediator from Ramatis III, and the Enterprise carries him to the planet. Riva is deaf and speaks through a chorus of three telepathic interpreters. At the first meeting a Solari who rejects the truce opens fire and kills the chorus, and is then shot by his own leader.
Riva is left unable to communicate and nearly gives up. With encouragement from Troi he decides to stay on Solais V alone and teach both sides his sign language, reasoning that learning to talk to him will teach them to talk to each other.