Dagon appears in HP Lovecraft's tales of horror as a loathsome fish-like monster, but the author took the name from that of an ancient Semitic god of grain and the harvest, who wasn't one of the bad guys at all.According to my old copy of The Concise Mythological Dictionary by Peerage Books, Dagon is the Hebrew spelling of an ancient god of the Philistines, Dagan, which translates as "grain".
The description of Dagon on www.godchecker.com/states says he is the "Inventor of the Hebrew Plow, before it plowed itself into becoming a Plough if not a Pluff."
According to Wikipedia, the fishy version of Dagon makes a number of modern fiction and movie appearances, including in Conan the Destroyer, Buffy the Vampire Slayer, Terry Pratchett's Discworld novels and Pinky & The Brain, as well as in tales by HP Lovecraft.
The Concise Mythological Dictionary
Omnibus: At the Mountains of Madness and Other Novels of Terror No. 1 (H.P. Lovecraft Omnibus)
The Call of Cthulhu: And Other Weird Stories (Penguin Modern Classics)
Grimoire of the Necronomicon
Call of Cthulhu (Call of Cthulhu Roleplaying) (Call of Cthulhu Roleplaying)