Who stole the ring in The Lord of Rings?

The One Ring was originally forged by the Dark Lord Sauron in Mount Doom, and it was never truly "stolen". However, it was taken from Sauron by the Elf Isildur after the defeat of Sauron at the end of the Last Alliance of Elves and Men.

Isildur cut the ring from Sauron's hand with his sword, but he was tempted by its power and decided to keep it for himself. This ultimately led to his demise, as he was ambushed and killed by Orcs while crossing the River Anduin. The One Ring was lost for centuries until it was discovered by Gollum.