Tarpok

Tarpok, along with Scibus, was a Silurian companion of Icthar, the sole survivor of the Silurian Triad.

In 2084 they 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)