What is the name of the realm ruled by Thranduil?

The realm ruled by Thranduil is the Woodland Realm. In Tolkien’s legendarium, it is the woodland kingdom of the Silvan Elves in the great forest east of the Misty Mountains.

The forest was originally called Greenwood the Great, but Sauron’s influence from Dol Guldur corrupted it, and it became known as Mirkwood. Thranduil’s father, Oropher, established the Elven kingdom there, and Thranduil became its king after Oropher died in the War of the Last Alliance against Sauron.

Readers often encounter several names for the same setting. “Mirkwood” primarily identifies the forest, while “Woodland Realm” identifies the Elven kingdom within it. Thranduil’s underground halls were in the forest’s north-eastern region, near Erebor, Dale, and Lake-town. His son Legolas was one of the realm’s most famous inhabitants.

After Sauron’s defeat, Thranduil and Celeborn cleansed the forest of evil, and it was renamed Eryn Lasgalen, meaning “Wood of Greenleaves.”