Cthulhu is an ancient, malevolent deity that's part of a pantheon of ancient and powerful beings known as the Great Old Ones. It's often depicted as a massive, octopus-like creature with a humanoid body, dragon-like wings, and a head resembling a combination of an octopus and a dragon. Cthulhu is said to be so immense that its awakening could bring about the end of the world.

According to HP Lovecraft's mythology, Cthulhu resides in the submerged city of R'lyeh, located in the South Pacific. The city is described as a nightmarish and non-Euclidean place, where Cthulhu and other Great Old Ones rest in death-like slumber, awaiting the time when they will rise again to dominate the Earth.