Shub-Niggurath, often associated with the phrase “The Black Goat of the Woods with a Thousand Young”, is a deity in the Cthulhu Mythos of H. P. Lovecraft. The creature is sometimes referred to as “The Black Ram of The Forest with a Thousand Ewes,” lending a male gender to the entity that is often thought of as female.
Shub-Niggurath is first mentioned in Lovecraft's revision story "The Last Test" (1928); she is never actually described in Lovecraft's fiction, but is frequently mentioned or called upon in incantations. Most of her development as a literary figure was carried out by other Mythos authors, including August Derleth, Robert Bloch and Ramsey Campbell.
August Derleth classified Shub-Niggurath as a Great Old One, but the Call of Cthulhu role-playing game classifies her as an Outer God. The CthulhuTech role-playing game, in turn, has returned to Derleth's classification of Shub-Niggurath as a Great Old One.
Read more about Shub-Niggurath: Development, The Black Goat, Robert M. Price's Interpretation