Question: how are tom riddle and harry potter related?
Answer: And the grandfather of Tom Riddle, Marvolo Gaunt proved that he had the Resurrection Stone was his in Bob Ogden's memory. Thus he and Tom were descendant of Cadmus Peverell. Cadmus and Ignotus were brothers, thus Harry and Voldemort are related in this way. ... Thus Voldemort's blood had Harry's blood in it too.