J.R.R. Tolkien’s fictional creator of the One Ring was Sauron.
Sauron forged the One Ring in the fires of Mount Doom during the Second Age. He created it to control the other Rings of Power and to extend his influence over their bearers. The Ring contained much of his own power, which made its destruction essential to defeating him permanently.
Sauron was a Maia, a powerful spiritual being who originally served the Vala Aulë before being corrupted by Morgoth. After Morgoth’s defeat, Sauron became the principal enemy of the Free Peoples in the Second and Third Ages.
Celebrimbor made the Elven Rings, while Saruman was a wizard who later became Sauron’s ally. Morgoth was Sauron’s earlier master and a greater primordial enemy. These overlapping roles are why the names are sometimes mixed up.