Dagon

Dagon (a.k.a. Father Dagon) is one of the Great Old Ones in the Cthulhu Mythos and rules over a race of amphibious fish-like humanoid creatures called True Merrows (more commonly known as Deep Ones) who inhabit Earth's oceans.

Physical Characteristics
Dagon, more or less, appears as a much larger and monstrous version of a Deep One with various attributes reminiscent of a fish, such as the scaly skin, fins, and the bulbous eyes and towers over fifty feet in height. There is actually a theory stating that Dagon himself is a True Merrow given an upper class like status with how True Deep One are (age-wise) immortal and continuously grow during their life time and since Dagon has a size that dwarfs other True Merrows, Dagon could possibly be the oldest living True Merrow.

History
While not much is known about his origins, Dagon is one of the Great Old Ones and because of this high status, he and other Great Old Ones such as Mother Hydra and Cthulhu are often worshiped and praised by the Deep Ones. He and the True Merrows resides on Earth in the under water city of Y'ha-nthlei where they live a harmonious and prosperous life style. As time went on, Dagon and the Deep Ones began to be worshiped by various human cults such as a tribe of island-dwelling aborigines who treated them as if they were Pagan gods with the tribe committing to ritualistic blood sacrifices in exchange for gold and have their waters teeming with fish. This tribe and a few Deep Ones were killed by other neighboring tribes who had taken offense to the Pagan worship and the religion of Dagon. After the destruction of the tribe, a man named Abed Marsh brought the Dagon religion to the town of Innsmouth and converted the towns people, forming a cult called "The Esoteric Order of Dagon". Innsmouth committed to the same ritualistic sacrifices and exchange as the tribe and even began mating with Deep Ones as a mandatory law since this was how Deep Ones bred. The children of the townspeople would soon grow into Deep Ones themselves and join Dagon in Y'ha-nthlei.

Mystery
In H. P. Lovecraft's "Dagon", Dagon is shown to be hugging and bowing to a monolith of unknown origin on a sea bed that was risen from the ocean depths possibly by volcanic eruption. The monolith had various pictographs and hieroglyphics of creatures and deities resembling sea creatures such as the Deep Ones, Cthulhu, Mother Hydra and Dagon himself. The origin of the monolith and the reason Dagon hugs and bows to it are unknown.

Appearences

 * "Dagon" by H. P. Lovecraft (1919)
 * (mentioned) "The Shadow Over Innsmouth" by H. P. Lovecraft (1931)