Tolkien's endless cast of characters is one of the best and worst elements of the story of Middle-earth. There are enough iconic heroes and villains for everyone to have fifty favorites. On the other hand, most brains can't possibly store the full breadth of so many life stories. Look at Thranduil, a king among the Elves who wasn't important enough to earn a name in his early appearances.
The Hobbit and The Lord of the Rings feel like very different works when examined through a modern lens. Their consistent storytelling connects them, but their differences in tone make them feel distinct. Following the lives of characters who live for hundreds of years will reveal some interesting elements in the writing process.
Where was Thranduil at the End of The Hobbit?
Thranduil was known as Elvenking in The Hobbit. He's the king of the Elves that reside in a forested realm called Mirkwood. His home was relatively secluded, but his primary trading allies were decimated by the mighty Smaug. When Bilbo and a company of Dwarves cross into Thranduil's territory, they are apprehended by his guards. These tensions escalated when Smaug was slain. Thranduil and the people of Esgaroth demanded a portion of Smaug's hoard. Thorin and his Dwarves opposed them, but the battle was halted with the help of the wizard Gandalf. All Gandalf had to do to settle the dispute was point out the oncoming swarm of greater threats.
Thranduil's force of Elven spearmen and archers was one of the titular Five Armies at the legendary battle. They were an essential part of the battle plan and the largest army numerically. Thranduil's Elves operated one of the two mountain spurs that lined the only entrance to the Lonely Mountain. Both spurs eliminated large swaths of the oncoming Orcs, Bats, and Wargs, but their enemies still vastly outnumbered them. The tide of war didn't fully turn until the iconic Giant Eagles arrived. With them, the skin-changer Beorn arrived in the form of a giant bear. Their presence raised morale and helped to lead the charge that forced the Orcs to retreat. Mighty Beorn destroyed the strongest Orcs until he made his way to their leader, Bolg. The Orcs retreated into the Mirkwood, where most of them were killed by hidden archers and large spiders. Thranduil was rewarded for his aid with the 500 emeralds of Girion.
What did Thranduil do Before Lord of the Rings?
There is a 78-year gap between the Battle of the Five Armies and the War of the Ring. However, the Elves of the Woodland Realms enjoyed less than a decade of that peace. In 2951, Sauron openly returned to Mordor and announced his intentions to rebuild his old fortresses. His home in the Mirkwood is called Dol Guldur, and it was sitting unoccupied for a decade. As soon as Sauron returned, he sent three Ringwraiths to re-occupy Dol Guldur. This forced Thranduil to be an active player in the War of the Ring from its earliest moments. His involvement increased when Gollum was laid at his feet.
Gollum was one of Sauron's first victims after the Dark Lord returned to Mordor. Drawn by the forces of evil, Gollum was captured, imprisoned, and tortured for an unknown period. After Sauron gathered the information he needed, he set Gollum free, convinced that his presence would draw out the Ring. The Ranger Aragorn found Gollum in the woods shortly thereafter. Aragorn handed him over to Gandalf, who interrogated him as well. Gandalf then settled Gollum in the care of two Elves in Thranduil's kingdom. Gollum escaped with the help of some Orcs, leaving Thranduil to send an important message. Thranduil sent his son Legolas to Rivendell to inform Elrond that Gollum was on the loose. This led to Legolas's crucial role in the Fellowship.
What did Thranduil do After the War of the Ring?
Mirkwood fared extremely well during the war. Thranduil's forces repelled Sauron's hordes at every turn and stood strong against the Dark Lord. After his victory, Thranduil made a deal with Celeborn to redefine the borders of his domain. Thranduil allowed the southern chunk of Mirkwood to be renamed East Lorien and established his base of power in the north. The wide forest between the two lands was handed to the Beornings and the Woodmen who'd always inhabited it. Thranduil also renamed Mirkwood, dubbing it Eryn Lasgalen, the Wood of Greenleaves. Under his leadership, the forest flourished well into the Fourth Age. It's unknown when or if he left the throne or departed for the Undying Lands.
Thranduil is one of many powerful nobles in the realm of Middle-earth. He doesn't fit the criteria for a hero or a villain. He's something in-between. Thranduil did much to defeat Sauron in two wars and led his people to victory both times. Though his kingdom had to struggle without peace for a long time, it's hard to paint Thranduil as anything other than an Elf making the best of several bad situations.