Tarpok

Tarpok was a Silurian who served as the science adviser to the Silurian Triad. (PROSE: The Scales of Injustice) He and Scibus later travelled in a Silurian battlecruiser with Icthar, the leader and sole-survivor of the Triad.

In 2084, Icthar attempted to take over Sea Base 4 and start a nuclear war to wipe out humanity, but were defeated by the Fifth Doctor. Tarpok later died from exposure to hexachromite gas. (TV: Warriors of the Deep)