The Men of Leng (their true name are unknown) are a humanoid race that lives in the Dreamlands, a parallel oniric dimension, and are one of the principal antagonists of The Dream-Quest of Unknown Kadath, written by H.P. Lovecraft. They're mysterious "emissaries" or soldiers of the main history villain Nyarlathotep.
They're described, first, as enigmatic merchants wearing Arabic-like clothes and using jewelry around their heads, arms and chests. They also take with them scimitars and whips to intimidate the ones who tries to oppose their commerce. Only their eyes are let visible, and strangely they're entirely white, without pupils.
At the Plateau of Leng, one of the regions in the Dreamlands where the Men of Leng lives, they're true appearance are revealed as satyr-like humanoids, with goat legs and little horns above their head. Their lips cross the entire face from ear-to-ear, giving them as sadistic-like smile.
The Men of Leng appears at the beginning of Randolph Carter's journey, when he arrives at the coast of Dylath-Leen. They're described as rich merchants that negotiate slaves from other lands in exchange of jewelry with the people of Dylath-Leen. The human merchants says to Randolph that the Men of Leng are scary and it's better to him to ignore them. Carter, however, attempt to board stealthy inside one of Men of Leng's ships, and by doing so, he's taken to the Moon of Dreamlands, where is revealed that the Men of Leng serves to another superior race called Moon-beasts, those serves to Nyarlathotep in his Black Pharaoh avatar. With the help of a army of cats, Carter escapes from their base.
The Men of Leng them will appear another time closely to the end of Randolph's adventure, when of them take Carter to their actual habitat, the obscure Plateau of Leng, to meet a strange and enigmatic cult leader wearing a veil. Carter, luckily, escapes again and falls to the Underworld of this dimension.