To be honest, I don't know for sure. It could have been a forgotten author from centuries ago or a little-known scholar. The history of such terms can be quite obscure.
I'm not sure who was the first. Maybe it was some ancient philosopher or scholar, but I don't have the exact name.
It's a tricky question. The origin of using'mythos' to describe stories is hard to pinpoint exactly. It could have emerged in ancient Greek literature or some other early cultural context, but identifying the very first person is quite challenging.
Some of the best Cthulhu Mythos stories include 'Pickman's Model'. It's a story that plays on the idea of art and the grotesque, as the main character discovers the disturbing paintings of Pickman. 'The Whisperer in Darkness' is also a great one. It has a lot of elements of paranoia and the discovery of hidden, alien entities. In addition, 'The Haunter of the Dark' is worth mentioning. It builds on the atmosphere of dread and the presence of an ancient, evil force in an abandoned church.
Another great one could be 'At the Mountains of Madness'. It takes the reader on an Antarctic adventure where the characters uncover ancient and dreadful secrets related to the Cthulhu Mythos. It's full of Lovecraft's signature atmosphere of dread and the idea that there are things in the universe that man was not meant to know. It also gives a lot of background about the Elder Things which are important in the Mythos.
I also recommend 'The Shadow over Innsmouth'. This story has a great atmosphere. It follows a man who visits Innsmouth and gradually uncovers the town's dark and fish - like secrets. The idea of a town with a hidden and disturbing past, and the presence of the Deep Ones, makes it a very engaging Cthulhu Mythos story.
The theme of the power of the supernatural is common. In mythos, gods and goddesses possess extraordinary powers. In horror stories, vampires have the power of immortality and super strength. Also, the idea of a cursed or doomed place is seen in both. Think of the ancient tombs in Egyptian mythos that are often filled with curses, and in horror, there are places like the Overlook Hotel in 'The Shining' which is haunted and seems to doom those who enter. Transformation is another theme. In mythos, we have tales of humans turning into animals or vice versa. In horror, there are werewolves and other shapeshifters.
Mythos Fiction is a genre that often incorporates elements of mythology into fictional stories. It can draw from various mythologies like Greek, Norse, or Egyptian. For example, many modern fantasy novels use mythological creatures such as centaurs or mermaids which are from Greek and other mythologies. This genre allows authors to create new and exciting worlds by building on the rich tapestry of existing myths.
August Derleth also made significant contributions. He continued to develop the Mythos after Lovecraft's death. His works added new elements and stories that are considered important for those new to the Cthulhu Mythos.
There might be cultists as well. These are the followers of the Cthulhu - related entities. They are usually depicted as being fanatical in their beliefs and willing to do whatever it takes to serve their dark masters. They can be quite menacing as they try to carry out their rituals or stop the investigators from interfering.
Some of the best ones include 'The Call of Cthulhu'. It introduced the iconic Cthulhu entity, with its dark and otherworldly themes of a sleeping, monstrous god waiting to rise again. The atmosphere is thick with dread and mystery.
One interesting Mythos Effect fanfiction could be a story that focuses on a new character's journey within the Mythos Effect universe. Maybe a character who discovers a hidden power and has to navigate the complex politics and power struggles in that world.
One interesting cthulhu mythos fanfiction could be about a modern - day detective who stumbles upon an ancient cult related to Cthulhu. He slowly uncovers the dark secrets of the cult as he delves deeper into the mystery, with each discovery leading him closer to the brink of madness.