Gollum was called Sméagol before he found the One Ring.
Sméagol was a member of a river-dwelling people related to the Hobbits. On his birthday, he went fishing with his relative Déagol, who discovered the Ring in the Anduin. Sméagol wanted it, killed Déagol, and took the Ring for himself.
The Ring’s influence helped transform Sméagol into the creature later known as Gollum. He was eventually driven away from his people and lived for centuries beneath the Misty Mountains. His repeated “gollum” sound became the source of his later name.
Déagol is the person who found the Ring, not Gollum’s original identity. This distinction matters because their encounter explains both the Ring’s movement from Isildur’s line to Bilbo and the moral decline of Sméagol.