The forest formerly called Greenwood the Great is Mirkwood in J.R.R. Tolkien’s Middle-earth.
Greenwood the Great was an enormous woodland in the north of Middle-earth. During the Third Age, the growing influence of the Necromancer, Sauron, brought darkness and danger into the forest, and it became known as Mirkwood. The change in name reflects both the physical threat and the corruption associated with Dol Guldur in the southern part of the wood.
Mirkwood is prominent in The Hobbit. Bilbo and the company of Thorin Oakenshield cross it during their journey to the Lonely Mountain, encountering giant spiders and the Elvenking’s halls. The forest also appears in the wider history of the War of the Ring.
Mirkwood is sometimes confused with Fangorn Forest, which is associated with the Ents, or Lothlórien, the woodland realm of Galadriel and Celeborn. After Sauron’s defeat, the forest was renamed Eryn Lasgalen, meaning Wood of Greenleaves.