Icthar

Icthar was the sole survivor of the Silurian Triad.

Following his revival into a world dominated by humans, Icthar decided, with his companions Scibus and Tarpok, to take over Sea Base 4 with Sea Devil troops and a Myrka, and trigger a nuclear war between two human factions. The Doctor had met Icthar before this incursion, having tried to mediate between the Silurians and humanity. The Fifth Doctor believed him to be killed, but he had not. After recovering from hexachromite gas poisoning, Icthar shot and killed Commander Vorshak with a Sea Devil weapon. Turlough then forced the weapon from Icthar, and killed him with it. (TV: Warriors of the Deep)

Behind the scenes

 * Some fans  commonly associate Icthar with the "Silurian Scientist" seen in the TV story Doctor Who and the Silurians. The Warriors of the Deep novelisation suggests a Doctor Who and the Silurians appearance of Icthar, although Icthar is simply described in the Warriors novelisation as a Silurian other than "Old Silurian" and "Young Silurian" who said little, which does not appear to synch up with the characterisation or dialogue of "Silurian Scientist". The novelisation also changes Icthar's line from the TV story about his Silurians offering a hand of friendship to the humans which led to a treacherous attack to one where the Doctor says he tried to offer peace between the two races, but failed because of the destructive efforts of extremists on both the human and Silurian sides.
 * The Target novelisation of Doctor Who and the Silurians, Doctor Who and the Cave-Monsters, does not name the scientist, Old Silurian or Young Silurian as "Icthar", but respectively as K'to, Okdel and Morka.
 * Additionally, Icthar appears in the novel 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.