At the age of 16( 1943), he came to Gunter's old house, knocked out his uncle Morfin Gunter, killed his old tom riddle and his old couple with Morfin's wand, and framed Morfin. Most importantly, he stole Marvolo Gaunt's ancestral treasure-a black stone ring engraved with "Pei Flier heraldry" (actually a symbol of the deathly Hallows, but tom riddle didn't know it was a resurrection stone). Later, he made the ring into a horcrux and hid it in Gunter's old house in Little Hangleton. He used a lot of powerful magic to protect it.
It is worth mentioning that during his stay at Hogwarts, he found himself a descendant of Slytherin, and saw a book "Secrets of Cutting-edge Dark Magic" from the library of Hogwarts, which described in detail the method of making horcruxes, so he sprouted the idea of making horcruxes, because horcruxes can make people live forever. He chose a diary to carry a fragment of his soul as the key to open the chamber of secrets next time. He "charmingly" discovered the whereabouts of Ravenclaw's lost crown from Ravenclaw's ghost Helena Ravenclaw, the daughter of rowena ravenclaw, the founder of Ravenclaw College. The crown was hidden in a hollow tree in a dense forest in Albania, and then when Voldemort came to Hogwarts to apply for the position of professor of defense against the dark arts, he hid it in the room of requirement. The obsession with power, the worship of pure blood, the fear of death and so on. There is no doubt that all this has taken him to an extreme.