Disillusioned Death Eater Regulus Black learned about the Horcrux and its hiding place. In an effort to bring about Voldemort's eventual downfall, he and his house elf Kreacher broke through the magical protection and stole the locket. While Black died in the effort, killed by the surrounding inferi, Kreacher took the locket back to their home at Number Twelve, Grimmauld Place. Kreacher continued to protect the locket for years. However, while the Order of the Phoenix was using the house as its headquarters, the locket was stolen by Mundungus Fletcher, a petty criminal and member of the Order. He gave it to Dolores Umbridge as a bribe when she caught him selling stolen property.
Two years later, Harry, Ron, and Hermione infiltrated the Ministry of Magic, where Umbridge worked, and stole the locket. Ron later saved Harry from being strangled by the locket. The Horcrux inside assumed the shape of Harry and Hermione and played on Ron's fear that Harry and Hermione had started a relationship during his absence (and his longer-held fear that in Hermione's eyes he, Ron, would never match up to Harry). The Horcrux attempted to possess him, but Ron overcame its influence and destroyed it using the sword of Godric Gryffindor.
After the release of the final book, several reviews noted similarities between Slytherin's locket and the One Ring from The Lord of the Rings, as both artifacts negatively affect the personality of those who wore them.