Nyarlathotep first appeared in the 1920's and is described as resembling an ancient Egyptian Pharaoh. In his first story, he is shown wandering the Earth in search of gathering followers through magical, Tesla-like instruments. The followers lose their awareness of the world and there is an impression that the all has collapsed and that the apocalypse has come. After this, Nyarlathotep is reputedly depicted as the harbinger of the earth's end.
Nyarlathotep is a major character in the story "The Dream-Quest Of Unknown Kadath" in which he manifests into the form of an Egyptian Pharaoh and confronts the character Randolph Carter. In "The Dreams In The Witch House" (1933), he appears to Walter Gilman and the witch Keziah Mason in the form of the 'Black Man', a black-skinned form of the Devil. He is also mentioned in "The Rats In The Walls" as a faceless god in Earth's center. Furthermore,
"The Haunter of The Dark" showcases a bat-winged, three-eyed monster in the steeple of a cult-church that is said to be Nyarlathotep.
Whereas most Outer Gods are ambivalent to, or unaware of humanity's existance, Nyarlathotep is unique in that he delights in causing suffering to humans.
It has been suggested that Stephen King's Randall Flag is among the avatars of Nyarlathotep.
Nyarlathotep is an omnipotent demonic deity. Just his presence alone can cause insanity. He is the messenger of the Other Gods and Azathoth, his father. His form as the Black Pharaoh is the abstract of chaos. He enjoys madness, and inflicts mortals with it. He is effectively immortal.
He can manifest to 1,000 forms, all reputed to be maddening and horrific.