Sometime after the events of book 5, and before the events of book 6. In other words, during Harry's vacation. about 1996 in says in the book
Marvolo Gaunt was a pure-blood wizard and descendant of Salazar Slytherin. He was the maternal grandfather of Tom Marvolo Riddle,
In 1996, Albus Dumbledore retrieved the ring, eventually destroying it with Godric Gryffindor's Sword.
it is one of the 7 horcruxes that are needed by harry to finally destroy voldemort
Marvolo Gaunt was Voldemort's grandfather.