Lord Voldemort
Harry looks into Snape's memories and finds out that Snape was a secret spy working for Dumbledore because Snape was in love with Harry's mother. In the memories, it is also revealed that Harry is an "accidental Horcrux" because a part of Voldemort's soul lives in him. Harry willingly lets Voldemort kill him, but Voldemort's killing curse instead destroys the part of himself inside Harry, meaning that Harry himself survives.