Short answers, pulled from the story.
The One Ring is a central plot element in J. R. R. Tolkien's The Lord of the Rings (1954-55), forged by the Dark Lord Sauron during the Second Age to dominate the other Rings of Power and control the free peoples of Middle-earth. It first appeared in The Hobbit (1937) as a simple invisibility ring before Tolkien expanded its role and rewrote parts of The Hobbit to fit the larger narrative.
The One Ring could only be destroyed in the fires of Mount Doom, the volcano where it was forged. During the quest, Frodo claimed the Ring for himself at the summit, but Gollum bit off Frodo's finger to take it back and then fell into the fires of Mount Doom, destroying the Ring and ending Sauron's power permanently.
The One Ring's primary power was control over the other Rings of Power and domination of their wearers' wills. It also conferred invisibility on mortal wearers, extended a possessor's life indefinitely, amplified any inherent power its bearer possessed, and could change size to escape its wearer. Within Mordor, a bearer could draw on its power even without wearing it.
Tolkien drew on the Völsunga saga, which he read in the 1870 translation by William Morris and Eiríkur Magnússon, and the Middle High German Nibelungenlied, both of which feature a cursed magical ring. These same sources underlie Richard Wagner's opera cycle Der Ring des Nibelungen. Tolkien also studied a 4th-century Latin curse inscription at a pagan temple in Lydney Park, Gloucestershire, concerning a stolen ring and the god Nodens.
Tolkien explicitly rejected allegorical readings, distinguishing between allegory, which he said resided in "the purposed domination of the author", and applicability, which "resides in the freedom of the reader". He argued that if The Lord of the Rings had been written as an allegory of World War II, the Ring would have been seized and used against Sauron rather than destroyed, and the outcome would have been continued war rather than peace.
The unique One Ring card from the Lord of the Rings-themed Magic: The Gathering set was purchased by the singer Post Malone for US$2 million, making it one of the most expensive collectible card game cards ever sold. The card was printed with its own artwork and Tengwar text, with only one copy in existence.