N'Gabthoth is an Old One who had been sleeping in a cavern in the ocean near Starkesboro for an unknown amount of time. When Dr. Strange killed Sligguth (one of the spawn of Set and an agent of Shuma-Gorath, N'Gabthoth woke from his slumber. He headed toward Ebora and the Serpent Men of Starksboro, to feed on the human sacrifices which they prepared for him. Who were freed by Dr. Strange during the fighting.
The Old One had the ability to survive both underwater and on land. N'Gabthoth could fire extremely powerful mystical bolts from his eye, a single one being able to knock out Dr. Strange out of the sky. He outmatched Dr. Strange in power, and was able to dissipitate magical spells. When the Ancient One added his own power to that of Dr. Strange, the Sorcerer Supreme was able to kill the Old One.