As revealed in the fourth season episode "Jump the Shark," John slept with a woman he met while away on a hunt. Learning over a decade later that he had fathered her son Adam, John made occasional visits over the years to partake in father-son activities with him. He hid the truth from Adam to protect him, and never revealed to him the existence of Sam and Dean, nor vice versa. Meanwhile, John trained Sam and Dean to become hunters. However, Sam later left this life to start anew in college, leading to a fallout between John and his son.