Visian

Visians were an invisible species of predators native to Mira.

Biology
According to the First Doctor, the Visians were about eight feet tall, "vicious", and the only sentient species indigenous to Mira. The pattern of their footprints seemed to indicate that they were bipeds. When exterminated by Daleks they were briefly visible and seemed to have a roughly humanoid form.(TV: The Daleks' Master Plan)

History
In the year 4000, the Visians attacked the Doctor, Steven and Sara Kingdom, who had been transported there against their will. They also attacked a group of Daleks who had come to the planet in pursuit of the Doctor. Their combat with the Daleks allowed the Doctor and his companions to escape Mira in a stolen Dalek ship. (TV: The Daleks' Master Plan)