Stalin's first wife, Ekaterina Svanidze, died in 1907, only four years after their marriage. At her funeral, Stalin allegedly said that any warm feelings he had for people died with her, for only she could melt his 'stony heart'. To him, her life was the only thing that made him happy. They had a son together, Yakov Dzhugashvili, with whom Stalin did not get along in later years.
His son finally shot himself because of Stalin's harshness toward him, but survived. After this, Stalin said "He can't even shoot straight". Yakov served in the Red Army during World War II and was captured by the Germans. They offered to exchange him for Fieldmarshal Paulus, but Stalin turned the offer down, allegedly saying "A lieutenant is not worth a general"; others credit him with saying "I have no son," to this offer, and Yakov is said to have committed suicide, running into an electric fence in Sachsenhausen concentration camp, where he was being held.
http://en.wikipedia.org/wiki/Joseph_StalinHe didn't kill him.