You've got to be referring to Gollum, the first keeper of the ring. Possession of the ring over time warped both his mind and body, and his one obsession is to get it back. He finally does manage to wrest the ring from Frodo's hand but in doing so loses his balance and plunges headlong, along with the ring, into the firey pit of Mordor. The way the story is presented suggests that this was Gollum's predestined fate and role - to bring about, though unwillingly, the destruction of the infamous ring.
Gollum and Smeagol is the name. The first person to gain the ring after humans lost it. Smeagol was a hobbit who, influenced by the ring, became twisted and ageless. The ring formed the personality of Gollum inside of him. Gollum hid from everyone and forgot real food, friends, and comfort. The ring became his only thing, his only friend, his precious.