Born on March 17, 1942, in Chicago, Illinois, the son of Danish and Polish parents, Gacy and his siblings grew up with an alcoholic father who often beat his children with a razor strap when they misbehaved.
Apparently, Mrs. Gacy was also subject to similar physical abuse from her husband. According to John's sister Karen, the siblings quickly learned to toughen up to these regular beatings and a young Gacy refused to cry underneath the hands of his abuser.
Suffering from a congenital heart condition as a child, this was simply another reason Gacy was seen as a failure in his father's eyes. This medical condition made the boy unable to play with other children and this alienated him from his peers.
He would soon realize he was attracted to men which challenged him mentally about his sexuality. At the time, being a homosexual simply wasn't an option in a then conservative society. All of these circumstances were a recipe for disaster as a young John struggled to fit in as he grew into adulthood.
As Gacy continued to age, he began to show signs of a tendency towards sadism, or, deriving pleasure and sexual gratification by inflicting pain, suffering, or humiliation on innocent victims.
In the late sixties, Gacy had several encounters with the law in relation to these offenses. In 1968, he was convicted of sexually assaulting a teenage boy, sentenced to a stint in the State Men's Reformatory (Anamosa State Penitentiary), and ordered to undergo a psychological evaluation.
Attempts at healing his disturbed mind and behaviors didn't go well. Following his release in 1970 and still on parole for this offense, he was again arrested for sexual assault. The charges would later be dropped, and Gacy went on to become a fairly successful independent contractor, purchased a home in suburban Chicago and it seemed as though he turned his life around.
Previous to working as a contractor, Gacy managed a fast-food restaurant in the 1960s. Later he became a Democratic precinct captain in the Chicago suburbs during the 1970s. He was well-liked in the community and neighbors looked at him as a helpful, friendly, normal guy.
Gacy also organized cultural events and gatherings in the area along with being involved with a local Jaycees civic group. His involvement in the community finally got him to blend in with his surroundings. Married and divorced twice, he had two biological children in addition to a pair of stepdaughters. This gave him the outward appearance of being a trusted, local, and familiar family man.