Gollum is a fictional character in J. R. R. Tolkien's Middle-earth legendarium. He was introduced in the 1937 fantasy novel The Hobbit, and became important in its sequel, The Lord of the Rings. Gollum was a Stoor Hobbit of the River-folk who lived near the Gladden Fields. In The Lord of the Rings it is stated that he was originally known as Sméagol, corrupted by the One Ring, and later named Gollum after his habit of making "a horrible swallowing noise in his throat".

Tolkien's monsters are the evil beings, such as Orcs, Trolls, and giant spiders, who oppose and sometimes fight the protagonists in J. R. R. Tolkien's Middle-earth legendarium. Tolkien was an expert on Old English, especially Beowulf, and several of his monsters share aspects of the Beowulf monsters; his Trolls have been likened to Grendel, the Orcs' name harks back to the poem's orcneas, and the dragon Smaug has multiple attributes of the Beowulf dragon. The European medieval tradition of monsters makes them either humanoid but distorted, or like wild beasts, but very large and malevolent; Tolkien follows both traditions, with monsters like Orcs of the first kind and Wargs of the second. Some scholars add Tolkien's immensely powerful Dark Lords Morgoth and Sauron to the list, as monstrous enemies in spirit as well as in body. Scholars have noted that the monsters' evil nature reflects Tolkien's Roman Catholicism, a religion which has a clear conception of good and evil.