Thranduil (The ElvinKing) first appears in The Hobbit as the Elvenking, when Bilbo and the Dwarves enter his realm in the northern part of Mirkwood. The Dwarves are captured by Thranduil’s guards and locked in his dungeons when they refuse to divulge their intentions. The Dwarves were rescued by Bilbo, who had remained in hiding with his use of a magic ring of invisibility.
After the death of the dragon Smaug, Thranduil along with people of Lake Town demanded a share of the treasure of Erebor. War with the Dwarves was averted by the arrival of a goblin/warg army and the ensuing battle.
Thranduilwas the father of Legolas, a supporting character in The Lord of the Rings. The gradually-established friendship between Legolas and the Dwarf Gimli, the son of Glóin of The Hobbit, helps to reconcile Thranduil’s people and the Dwarves.
The appendices to The Return of the King note that Thranduil withstood attacks by Sauron during northern battles of the War of the Ring, meeting with Celeborn and his people to together destroy Dol Guldur and cleanse Mirkwood of Sauron’s taint of evil. Also, Legolas and the Silvan Elves later worked together with Gimli and the Dwarves to rebuild and improve Minas Tirith, capital city of Gondor, the realm of their mutual friend Aragorn. The last time Thranduil was mentioned was soon after Sauron’s final defeat.