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 Smeagol, he was corrupted by the One Ring and later named Gollum after his habit of making "a horrible swallowing noise in his throat".
Bilbo Baggins is the title character and protagonist of J. R. R. Tolkien's 1937 novel The Hobbit, as well as a supporting character in The Lord of the Rings. In Tolkien's narrative conceit, in which all the writings of Middle-earth are translations from the fictitious volume of The Red Book of Westmarch, Bilbo is the author of The Hobbit and translator of various "works from the elvish" (as mentioned in the end of The Return of the King). In the Hobbit, he encounters Gollum in a goblin cave and finds the One Ring.
Frodo Baggins is a fictional character in J. R. R. Tolkien's legendarium, and the main protagonist of The Lord of the Rings. Frodo is a hobbit of the Shire who inherits the One Ring from his cousin (referred to as his uncle) Bilbo Baggins and undertakes the quest to destroy it in the fires of Mount Doom. He is also mentioned in Tolkien's posthumously published works, The Silmarillion and Unfinished Tales. Of all the ring-bearers, Frodo suffers the most and has his finger bitten off by Gollum at Mt. Doom.
Samwise "Sam" Gamgee is a fictional character in J. R. R. Tolkien's legendarium. Samwise is one of the supporting characters of The Lord of the Rings, in which he fills an archetypal role as the sidekick of the primary protagonist, Frodo Baggins. In the Return of the King, he finds the One Ring and takes on the task of disposing of it in Mt. Doom upon assuming that Frodo is dead. Later he frees Frodo and hestitantly returns the ring to him. Like Gollum, Bilbo and Frodo, he is a ring-bearer that leaves Middle-Earth.