UNCANNY X-MEN (1963) #12

Professor X reveals something about his past as a child: after the death of his father during a nuclear accident in Alamagordo, Dr. Kurt Marko (a friend of his father) married Xavier’s mother Sharon to help raise him, and to take control of Xavier’s money. Dr. Marko had already a boy, Cain Marko, an evil boy that always bullied Xavier. When Xavier discovered his mental powers he became very good in everything, from classes to sports because of his powers. Cain was always jealous about Xavier.…