Voldemort's father was a muggle who lived in the town where his mother was shunned because her family was poor and just plain creepy. After Voldemort's uncle and grandfather were arrested, his mother Merope placed some kind of spell on Tom Riddle senior to make him fall in love with her. When Merope was pregnant with Voldemort, she took the spell off of his father, and Tom Riddle senior left her. With no momeny and no place to go, Merope left the then infant Tom Riddle (aka Voldemort) at an orphanage where he was raised until he went to Hogwarts. He found out his father's side of the family were muggles and he killed them because of his hatred for the non-magical world. Another reason he killed them was to make a Horcrux, which is an item that houses part of your soul to keep you from dying. Because of his pathological fear of death and dying, Voldemort created seven of these items.(His snake Nagini, Slytherin's locket, His diary, Hufflepuff's cup, Ravenclaw's Diadem, his grandfather's ring, and Harry Potter himself). Harry Potter was not meant to be a Horcrux. Voldemort's soul was already so unstable at the time of the Potter's murders, that when he tried to kill Harry, a fragment of his soul attached itself to Harry, which is the reason why he didn't die like his parents. To create a horcrux, it require a supreme act of evil, which explains the murders Voldemort had committed. Since creation of Horcruxes involves mutilation of your soul, your body becomes less human, which also explains the way Voldemort looks today.