Azal

Azal was the last living Dæmon. Thousands of years prior to the 20th century, he placed himself in suspended animation in his spacecraft under Devil's Hump until the time came to judge if the Dæmons' experiment with humanity were a success or a failure.

Biology
Azal was a satyr-like humanoid with reddish skin and thick fur. He had sharp fangs, pointed ears, a thick beard and long horns. His legs were goat-like with cloven hooves. He was around thirty feet tall naturally, but he could change his size with his technology. (TV: The Dæmons)

Biography
An attempt to awaken Azal in 18th century Japan was thwarted by the intervention of the Fourth Doctor and Leela. (AUDIO: Time in Office)

In the late 20th century, awoke Azal, planning to have the Dæmon pass on his power to him. Azal instead offered his power to the Third Doctor, who refused. When Azal decided to kill him, Jo Grant offered to take his place. Azal, unable to comprehend this seemingly irrational act of self-sacrifice, self-destructed. (TV: The Dæmons)

A Northern Irish UNIT soldier named Francis Cleary was driven mad after seeing the Devil himself in Devil's End. (PROSE: Who Killed Kennedy)

Other references
When the Skith Leader scanned the Tenth Doctor's mind, Azal was among the alien creatures shown to him. (COMIC: The First)