Déagol was a friend of Sméagol, among a riverside people of hobbit-kind who lived near the Gladden Fields on the Great River, long before the hobbits came to the Shire. Gandalf told his story to Frodo, having pieced it together from what he forced out of Gollum.1
Déagol went fishing in a boat on the Anduin, while Sméagol, who said later that it was his birthday, walked on the bank. A great fish took Déagol's line and dragged him into the water, and on the river-bed he saw something shining. When he came up, he had a gold ring in his hand.1
Sméagol watched him from behind a tree, and asked for the ring as a birthday present. Déagol said he had given Sméagol a present already, and that he was keeping this one. So Sméagol caught him by the throat and strangled him, and took the ring. That was how the One Ring, lost since Isildur fell at the Gladden Fields, came back into the world, about the year 2463 of the Third Age.1,2
The idea that the ring had been a birthday present stayed with Gollum. Bilbo overheard him muttering "My birthday-present!" in the dark, and his own first account of the finding was shaped by it.3,4
The names are among Tolkien's translations: Déagol and Sméagol render names in the old speech of the Northmen.5
Sources
Citations name the chapter rather than the page, so they work in any edition. The colour of each note shows what kind of source it is.
- Published story The Hobbit and The Lord of the Rings as Tolkien published them.
- Appendices Tolkien's own appendices to The Lord of the Rings.
- Published story The Fellowship of the Ring, Book I, ch. 2, “The Shadow of the Past”
- Appendices The Lord of the Rings, Appendix B, “The Third Age”
- Published story The Hobbit, ch. 5, “Riddles in the Dark”
- Published story The Fellowship of the Ring, Prologue, 4, “Of the Finding of the Ring”
- Appendices The Lord of the Rings, Appendix F, II, “On Translation”