Dean is Mary's first born child, so unlike Sam, Dean had the luxury of having Mary around and caring for him. When Mary and John had tough times, Dean would cheer her up. When Dean was about 2-3 years old, John moved out for a couple of days due to a fight. After talking to him on the phone, Mary would get upset and Dean went and hugged her to tell Mary that John still loved her. Dean last saw her alive when he was four, when John brought him in to Sam's nursery to say goodnight to Sam. Mary was then killed by Azazel. Dean later joins his father on a crusade to find the thing that killed her.