Nyarlathotep (the Crawling Chaos)
Nyarlathotep differs from the other beings in a number of ways. Most of them are exiled to stars, like Yog-Sothoth and Hastur, or sleeping and dreaming like Cthulhu; Nyarlathotep, however, is active and frequently walks the Earth in the guise of a human being, usually a tall, slim, joyous man. Most of them have their own cults serving them, while Nyarlathotep seems to serve them and take care of their affairs in their absence. Most of them use strange alien languages, while Nyarlathotep uses human languages and can be mistaken for a human being. Finally, most of them are all powerful yet purposeless, yet Nyarlathotep seems to be deliberately deceptive and manipulative, and even uses propaganda to achieve his goals. In this regard, he is probably the most human-like among them.
Nyarlathotep enacts the will of the Outer Gods, and is their messenger, heart and soul; he is also a servant of Azathoth, whose wishes he immediately fulfills. Unlike the other Outer Gods, causing madness is more important and enjoyable than death and destruction to Nyarlathotep. In this sense, he strongly resembles the traditional role of the devil.
Nyarlathotep has many forms (some literature refers to these forms as Masks and claims that he has a thousand of them) and is thus known by different avatars.
And it was then that Nyarlathotep came out of Egypt. Who he was, none could tell, but he was of the old native blood and looked like a Pharaoh. The fellahin knelt when they saw him, yet could not say why. He said he had risen up out of the blackness of twenty-seven centuries, and that he had heard messages from places not on this planet. Into the lands of civilisation came Nyarlathotep, swarthy, slender, and sinister, always buying strange instruments of glass and metal and combining them into instruments yet stranger. He spoke much of the sciences - of electricity and psychology - and gave exhibitions of power which sent his spectators away speechless, yet which swelled his fame to exceeding magnitude. Men advised one another to see Nyarlathotep, and shuddered. And where Nyarlathotep went, rest vanished; for the small hours were rent with the screams of a nightmare.
—H.P. Lovecraft, "Nyarlathotep"