Icthar

Icthar was one of a Triad of Silurian leaders.

Following his revival into a world dominated by humans, Icthar decided, with his fellows, to take over Sea Base 4 with Sea Devil troops and a Myrka, and trigger a nuclear war between two human factions. His familiarity with the Fifth Doctor suggests an earlier encounter. Turlough shot him with a Sea Devil weapon while he was recovering from hexachromite gas poisoning, he attacked and killed Vorshak as his last act. (TV: Warriors of the Deep)

Behind the scenes

Some fans commonly associate Icthar with the surviving member of the three Silurian leaders, "Silurian Scientist" seen in Doctor Who and the Silurians.
The Target novelisation, Doctor Who and the Cave-Monsters gives alternative names of all three and does not list Ichtar as one of the three.
Additionally, Icthar appears in the novel PROSE: The Scales of Injustice, which also establishes that Silurians belong to different races or sub-species, with Icthar belonging to a different sub-species than the one seen in Doctor Who and the Silurians.