Icthar

The Silurian 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 Doctor suggests an earlier encounter. (DW: Warriors of the Deep)

Behind the Scenes
While fans commonly associate Icthar with the surviving member of three Silurian leaders, "Silurian Scientist" seen in Doctor Who and the Silurians, the Target novelisation, Doctor Who and the Cave-Monsters gives the actual names of all three and does not list Ichtar as one of the three.

Additionally, Icthar appears in the novel MA: 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.