Ring Taken

By the time The Lord of the Rings opens, Gollum is a very old,
and completely broken in mind and spirit after many long centuries with the Ring.
Smeagol stayed there for many years until he was unexpectedly visited by Bilbo Baggins,

who found Smeagol's ring near the water where he had left it accidently.
Bilbo encountered Gollum and it was at this time the two of them engaged in the famous riddle contest

that Bilbo eventually won by challenging Gollum to answer the question,
"What have I got in my pocket?"
Gollum, unable to answer, lost the match,
but later deduced that it must have been his beloved ring which he called "My Precious".
Pained by the loss of his precious talisman,

and tortured by the enslaving hold it had on his body and mind,
Gollum was eventually driven to leave his dark sanctuary and seek Bilbo out.
This latter act proved to be one of the key events in the later history of the One Ring.