Alan Clark

Clark, along with Hickman, was a caretaker of an abandoned sea fort in the English Channel. They were attacked by Sea Devils, who killed Hickman, and when the Third Doctor and Jo Grant arrived, he was frightened nearly to insanity. He was the one who first called the reptiles "Sea Devils". (TV: The Sea Devils)

Behind the scenes
In the novelisation, he is given the first name of Alan.