Gollum
Gollum is a fictional character from J. R. R. Tolkien's legendarium. He was introduced in the 1937 fantasy novel "The Hobbit", and became an important character in its sequel, "The Lord of the Rings". Gollum was a Stoor Hobbit of the River-folk, who lived near the Gladden Fields. Originally known as Sméagol, he was corrupted by the One Ring and later named Gollum after his habit of making "a horrible swallowing noise in his throat".
Thranduil
Thranduil did what he could to aid his allies during the War of the Ring, including holding the creature Gollum in his dungeons for interrogation by Gandalf on the history of the One Ring. Gollum soon escaped with the aid of Orcs, and Thranduil sent his son Legolas to Rivendell to seek the counsel of Elrond and Gandalf on this and other matters. Thranduil and his people withstood attacks by Sauron's forces during northern battles of the war. Having routed their foes in the north, Thranduil's forces moved south, and joined with the armies of Lorien under Celeborn and Galadriel in destroying Dol Guldur, cleansing Mirkwood of Sauron's taint of evil, and Thranduil, along with Celeborn, renamed Mirkwood "Eryn Lasgalen", The Wood of Greenleaves. After the war, Thranduil's realm was expanded to include all Mirkwood north of its central mountains, and he and his people enjoyed peace. Whether he departed Middle-earth for Valinor is unknown.