King of Mirkwood and father of Legolas,Thranduil was a Sindarin prince that came from the west with his father Oropher in the Second Age. They established the kingdom of Greenwood the Great, which later became known as Mirkwood.

Along with his father, he fought in the Last Alliance of Elves and Men. When Oropher was lost in one of the first battles,Thranduil became king. He wished to recreate the glory of Doriath, from whence he came, and he started to build a cave hall to match Menegroth. However,due to the inappropriate terrain at Greenwood, the cave hall was not easy to make and so when it was finished, it looked nothing like Menegroth.

Thranduil sent his son Legolas to the Council of Elrond in TA 3018. When the War of the Ring ended, he met with Celeborn and agreed to cede South Mirkwood to Lothlórien. The region became known as East Lorien.

Thranduil then renamed Mirkwood Eryn Lasgalen, meaning "the forest of the greenleaves".

He had fondness for silver and white gems, and he wore a crown of leaves and berries that changed colour with the seasons. He wielded a carven staff of oak. His hair was golden.

How long he remained on Middle-earth is not known, but it is likely that he was the last Elven King there.