Triad

The Triad were the ruling authority of the Silurian people.

One Triad, which included Icthar, Scibus and Tarpok, freed their Sea Devil cousins and tried to take over Sea Base 4. They intended to start a nuclear war to wipe out humanity, but were all killed when the Fifth Doctor flooded the control room with Hexachromite gas. (TV: Warriors of the Deep)

The Silurian city beneath Cwmtaff was ruled by the Triad of the scientist Malohkeh, the leader of the warrior class, Restac, and the elder Eldane. Malohkeh was killed by Restac after she decided to exterminate the humans in the city. Restac was herself poisoned by fumigation gases released by Eldane, who did not wish for the humans to be slaughtered. (TV: Cold Blood)