Short answers, pulled from the story.
Gollum is a fictional character in J. R. R. Tolkien's Middle-earth. He was originally a Stoor Hobbit named Sméagol who murdered his cousin Déagol to obtain the One Ring, which then extended his life far beyond natural limits and corrupted his body and mind over centuries. By the end of the story, nearly 600 years old, he accidentally destroys the Ring by falling with it into the fires of Mount Doom.
The Tolkien scholar Douglas A. Anderson proposes that Tolkien derived the name from the Old Norse word gull or goll, meaning "gold, treasure, something precious", with gollum as its dative form. A second theory connects the name to golem, the creature of Jewish folklore. Gollum received the name from his hobbit relatives because of the horrible swallowing noise he made in his throat.
A span of 556 years separates Gollum's finding of the One Ring and its destruction, meaning he was almost 600 years old at the time of his death. An average hobbit lifespan is over 100 years. The Ring prolonged his life far beyond what would otherwise have been possible.
Andy Serkis voiced and performed Gollum through motion capture in Peter Jackson's Lord of the Rings and Hobbit film trilogies. The digital character was built by Jason Schleifer and Bay Raitt at Weta Digital around Serkis's facial features and acting choices. Serkis based Gollum's distinctive throat sound on the noise of his cat coughing up hairballs.
Scholars have compared Gollum to the monster Grendel and the dragon in Beowulf, to Gagool the ancient hag in Rider Haggard's 1885 novel King Solomon's Mines, to the subterranean Morlocks in H. G. Wells's 1895 novel The Time Machine, and to figures from the Völsunga saga and the Cain and Abel story in Genesis. The Tolkien scholar Verlyn Flieger calls Gollum Tolkien's central monster-figure.
Scene 29 of The Two Towers directly portrays Gollum's split personality as two separate characters in conversation, using a continuous camera arc followed by nineteen shot/reverse shots. Film scholar Kristin Thompson called it "perhaps the most celebrated scene in the entire film." The Tolkien scholar Tom Shippey described the arguing-with-himself scene as "especially good and original."