Each of Voldemort's 7 Horcruxes were important to his history ... and Harry first saw it in Order of the Phoenix while cleaning out Grimmauld Place. The golden trio tracked it down, and Ron ...

This Horcrux was first seen by Harry in Order of the Phoenix. Marvolo Gaunt, Voldemort’s maternal grandfather, was a direct descendant of Salazar Slytherin and held violent anti-Muggle beliefs.