Scibus
Scibus, along with Tarpok, was a Silurian companion of Icthar. According to one account, Icthar was the "sole survivor" of the Silurian Triad. (TV: Warriors of the Deep) According to another account, Scibus was himself one of the Triad and Icthar's "Second."
After waking on an Earth dominated by humans, Scibus told Chukk, the leader of one of the Silurian shelters, that his brother Okdel L'da's shelter had survived, and told Auggi D'jo that the former shelter of Auggi's widow Daurrix had also been awakened by human activity. He had intended to tell this to Daurrix himself but appeared to momentarily forget that Daurrix was dead. The Third Doctor pleaded with the Triad to seek peace with the human race, but this failed after a C19 operative killed Chukk. (PROSE: The Scales of Injustice)
In 2084, Icthar, Scibus and Tarpok tried to take over Sea Base 4 and start a nuclear war to wipe out humanity. They were defeated by the Fifth Doctor. Scibus died from exposure to hexachromite gas just after beginning the missile launch sequence. (TV: Warriors of the Deep)
