Dagon is a demon in Neil Gaiman's novel Good Omens. The name is a likely nod to the Great Old One Dagon.
Dagon was once an angel, who decided to took part in Lucifer's revolution, alongside 10 million other angels. All rebel-angels were cast into Hell, and became the demons.
In Hell, Dagon became known as the "Lord of the Files" and "Master of Torments".
Dagon likely influenced humanity over its history to create the ancient Mesopotamian and Canaanite Deity of the same name.