Nogad was a descendant of the Deep Ones, a race of fish-like beings. He believed that the Deep Ones should dominate the human race. He was defeated after the Ghostbusters managed to get The Deepest One to turn against him. Nogad tried to keep the creature from betraying him by saying that he needed him, but this only proved the Ghostbusters' point.
Nogad is "Dagon" spelled backwards, the name of a leader of the Deep Ones in the works of H.P Lovecraft.