Gollum, born as Smeagol sometime during the 2400s of the Third Age, was a native Hobbit who killed another Hobbit in order to acquire the One Ring. He was described as a small, slimy creature and was about 589 years old at the time of his death. In Middle-earth: Shadow of Mordor, the two main protagonists, Talion and Celebrimbor, met Gollum on his journey within Mordor.

Smeagol spent his early years with his extended family under the matriarch, his grandmother. He once lived in Vales of the River Anduin near Gladden Fields, where he was part of a group of Hobbits called Stoors. He was not well-liked by his family members. He only had one friend; a Hobbit named Deagol, whom he once went fishing with in the Anduin. Deagol found the One Ring at the bottom of the river while fishing, and immediately the Ring took over him with its spell, making him want it for himself. But Smeagol also wanted the Ring, Smeagol arguing that it was his own birthday, but Deagol would not give up the Ring. Smeagol strangled Deagol to death, taking the One Ring for himself.

Constant exposure to the Ring twisted Smeagol, ruining his body and twisting his mind. He developed two separate personalities, one representing what was left of Sméagol (dubbed "stinker" by Samwise Gamgee), and the other representing the malign influence of the Ring. Sméagol used the Ring for stealing from, spying on and antagonizing his friends and relatives. When he wasn't using it, he hid the ring in his throat, resulting in the distinctive choking sound he occasionally still makes. The townsfolk nicknamed him "Gollum" for that reason, and eventually banished him. He then made his way to an island at the center of an underground lake hidden deep within the Misty Moutains. He ate mostly cave fish to survive, which he caught from his small boat, but when he thought he could get away with it he used the Ring to hunt small goblins who strayed too far from the stronghold of the Great Goblin.

Gollum left his cave in pursuit of Bilbo a few years after losing the Ring, but the trail was cold. He made his way to the edge of Mordor, where he met the monstrous spider Shelob and became her spy, leading Uruk and other creatures into her nest in order to avoid becoming food himself.

During the events of Shadow of Mordor, Talion and Celebrimbor seek him out in order to shed light on the identity of the latter. When they locate him, Gollum swears to serve The Bright Master. While Celebrimbor believes he can be a valuable asset, Talion does not trust the creature.