Because he was deaf, to communicate, Riva used his Chorus of telepathic interpreters who spoke for him. The trio represented different aspects of Riva: the "Scholar/Artist", the "Warrior/Adonis", and "Culture Woman" who held the other two together.
Riva was well known for mediating several treaties between the Federation and Klingon Empire; in fact, before Riva, there was no Klingon word for "peace-maker". Up until stardate 42477, Riva had never failed at finding peace.
In 2365, he was to negotiate an end to hostilities on Solais V. He was transported to the negotiations by the Enterprise-D. Immediately upon meeting her, he was taken with the empathic Counselor Deanna Troi and asked her to join him for dinner that evening. She accepted and dined with Riva where she learned more about him. Riva was also fascinated with Geordi La Forge's blindness and his use of the VISOR.
During the first meeting his Chorus was killed by a member of a Solari faction who did not wish peace. With his normal means of communication gone, Riva felt he could not complete his mission. However, after some convincing by Troi, and with the assistance of Commander Data who learned his sign language so that he could function as an interpreter, Riva continued his work. Riva decided to bring the warring sides together and teach them sign language, which would help bond the factions and provide common ground to aid in negotiations. He stayed on Solais V to begin the process of peace. (TNG: "Loud As A Whisper")
Riva was played by Howie Seago, who is deaf in real life.
Seago petitioned the producers to create a show about deaf people to help dispel untrue and prejudiced myths about them. In the first draft, Riva learned to speak overnight after a mechanical translator he used to communicate with his Chorus failed. Seago suggested the ending used in the finished episode. (Star Trek: The Next Generation Companion 2nd ed., p. 73)