Mirkwood

First Age history
When the primeval Elves made their Great Journey westwards across Middle-earth to Beleriand and the Undying Lands, they encountered a large forest which they namedGreenwood the Great. Some of the Elves of the Teleri tribe decided to settle in this forest; these Elves came to be called Silvan Elves, or Wood-elves.

When Dwarves migrated into the region, they made a road which ran through the forest from east to west. This road was later known as the Old Forest Road or Old Dwarf Road.

Second Age history
In the early part of the Second Age, the Woodland Realm was established in Greenwood the Great by a lord of the Sindarin Elves who had migrated eastward from Lindon. The Woodland Realm was a mingling of two types of elves, Sindar coming from the ruin of Doriath, and the Silvan or Wood elves who had already been settled there. Oropher, who had chosen not to depart Middle-earth after the destruction of Beleriand, chose to settle in Greenwood the Great and was taken by the Silvan Elves as their Lord.

Third Age history
In The Hobbit, The Lord of the Rings, and associated writings, the expansive forest of Greenwood the Great was called Mirkwood. In this instance, the name is supposedly a translation of an unknown Westron name. Around the year 1050 of the Third Age, 'the shadow ofDol Guldur' fell upon it, and men began to call it Taur-nu-Fuin and Taur-e-Ndaedelos (Sindarin: forest of great fear). The shadow was the power of Sauron who, under a concealed identity, established himself at the fortress of Dol Guldur on Amon Lanc, a prominent hill in Southern Mirkwood. The presence of Sauron's minions drove the Elves (now led by Thranduil, son of Oropher) further northward, so that by the end of the Third Age they were a diminished and wary people who had entrenched themselves beyond the Mountains of Mirkwood. The Old Forest Road or Old Dwarf Road crossed the forest east to west, but due to its relative proximity to Dol Guldur, the road was mostly unusable. The Elves made a path farther to the north, which ended somewhere in the marshes south of the Long Lake of Esgaroth.

In The Hobbit, Bilbo Baggins, along with Thorin Oakenshield and his band of Dwarves — minus the Wizard, Gandalf — ventured into Mirkwood during their quest to regain Erebor from the Dragon Smaug. During their passage through Mirkwood, the party encountered and was captured by many Giant Spiders, descended from Shelob. Shortly after the dwarves' escape they were taken prisoner by the Elves and brought before Thranduil, who imprisoned the dwarves. While unclear, it was shortly after or possibly even during these events, that the White Council flushed Sauron out of Dol Guldur, and as he fled to Mordor his influence in Mirkwood diminished for a while.

Years later, Gollum, after his release from Mordor, was captured by Aragorn and brought as a prisoner to Thranduil's realm. Out of pity, they allowed the creature some freedom to roam the forest (under close guard). Gollum escaped custody during an Orc raid, and fled south to Moria in search of the One Ring.

After Sauron's destruction at the conclusion of the Third Age, Mirkwood was cleansed by Galadriel and became known as Eryn Lasgalen, Sindarin for the Wood of Greenleaves.