First and Second Ages
Thranduil was the only son of Oropher, the King of the Woodland Realm. He was born sometime during the late First Age in Doriath before its fall. At the beginning of the Second Age, the Sindar travelled east and Oropher eventually founded Greenwood the Great.
In SA 3434, Thranduil and his father fought in the Battle of Dagorlad. Oropher was slain and Thranduil returned to Greenwood with roughly a third of the army that had marched to war. He claimed his inheritance and some time before TA 1000 inherited Oropher's title of King of the Woodland Realm, reigning over the south of Greenwood the Great.