Cthulhu is a cosmic entity and one of the Old Gods, the first of The Dark Ones. Cthulhu is described as a giant being with a squid-like face, bat-like wings and claws. Many years ago in ages long past, Cthulhu tried to destroy the Multiverse because of his hatred for all life. He would've succeeded if The Council of Light hadn't stopped him. Cthulhu was then imprisoned in the underwater city of R'lyeh where he sleeps for all eternity. According to legend, if Cthulhu breaks free from his prison, it's the beginning of the end of the Multiverse. But over-time, Cthulhu became a myth and a fairy tale to scare bad kids and is long forgotten. However, he communicates with the outside world via nightmares and visions of monsters and the sunken city of R'lyeh. There's even a cult that worships Cthulhu as they perform sacrifices to the ancient monster.
- Cthulhu will appear in Sunset Shimmer's Adventures of Equestria Girls: Legend of Everfree, where he is released from the Wondercolt Statue along with Bill Cipher after Midnight destroyed it during battle from Twilight and Kyle's Adventures of Equestria Girls: Friendship Games.