Szlth'TOK

 was a member of a liquid species that existed on Earth long before the Silurias or humans. He tried to avenge the wrongs done to his people by the humans by killing everyone involved with the Svarozhich Project and destroying Prague. The Fifth Doctor helped Szlth'TOK and Director Abloran reach an agreement that would prevent a further loss of life. (PROSE: Men of the Earth)