Father Dagon is a Deep One that has grown to an enormous size, over 20 feet tall. Some writers have suggested that this would make it millions of years old. Others have suggested that this is not a unique individual, but a class of ancient Deep Ones. Dagon is sometimes mentioned in conjunction with a "Mother Hydra", which is supposed to be a female of similar size and aspect.
There is a Dagon that mentioned in the Old Testament of the Christian Bible that was worshipped by the Philistines. He was said to be a fish-god, though there is no clear link between it and the Mythos entity.