Gollum

Gollum also known as Sméagol (or Trahald), is a creature of Hobbit-like origin driven mad by the One Ring. He murdered his cousin for it and tried to justify it by telling himself that it was his birthday present.

When the Ring left him, he chased first "that nassssty Bagginses", Bilbo to get it back and later Bilbo's first cousin once removed, Frodo, to the very Cracks of Doom, where Gollum and Ring fell into the lava.