While we learned more about Voldemort's past in the sixth movie, they left out how much of an impact his parents had on him. In the book, Harry traveled to the House of Gaunt via Dumbledore's Pensieve and saw Voldemort's mother, Merope Guant. She was in love with a muggle named Tom Riddle, and she created a love potion so he'd feel the same way. After they got married and pregnant, she released the love potion, and her muggle husband became disgusted by her. Because Voldemort was conceived through magic and not love, we discovered why he can't feel for other people.