What is the name of the forest called Mirkwood in J.R.R. Tolkien’s The Hobbit before its corruption?

Before its corruption, the forest later called Mirkwood was known as Greenwood the Great.

Greenwood the Great was one of the major forests of Middle-earth. Over time, the Necromancer—later revealed to be Sauron—established himself at Dol Guldur in the southern part of the forest. His presence brought fear, disease, and shadow, and the name Mirkwood became associated with the transformed woodland.

The forest is a major setting in The Hobbit. Bilbo and the Dwarves cross it after leaving Beorn’s house, face giant spiders, and are captured by the Wood-elves. In The Lord of the Rings, its political and military history continues, and the forest is also connected with Thranduil’s realm and the wider struggle against Sauron.

Greenwood the Great is therefore the earlier name, while Mirkwood describes the later period of corruption. The forest’s changing name reflects Tolkien’s habit of showing how places acquire different identities through historical events.