Marvin Gayle Gray was born on August 7, 1954, in Princeton, Caldwell County, Kentucky. He was the seventh child in a large family with ten children. From a young age, Marvin experienced panic attacks starting at the age of four. This led to him taking medications with methamphetamines for seven years. Despite these challenges, he developed an interest in working in the tobacco fields and other labor-intensive jobs.

Marvin’s panic attacks subsided in 1965 when his father had a heart attack. After this, his mother took on the main responsibilities of caring for the children and managing the family's finances. With less supervision from his parents, Marvin’s behavior changed. He struggled in school, and his grades dropped significantly. At the age of 12, he was arrested for the first time. He was convicted of breaking into someone’s property and stealing, which resulted in him being sent to a juvenile facility.

In the juvenile facility, Marvin faced a tough environment. He described it as a place where the younger and weaker boys were often bullied and mistreated. This experience had a significant impact on him, leading to feelings of anger and resentment towards adults and authority figures. After serving time, he was released in 1968 and continued to have trouble fitting in. On his first day back at school, he brought weapons and threatened school officials, resulting in his expulsion.

In 1970, Marvin Gayle Gray began his criminal activities by stealing a weapon from a neighbor's garage. He quickly escalated to multiple thefts and attacks, using a pistol to threaten his victims. After his arrest, he faced charges of robbery, burglary, illegal possession of weapons, and making threats. In 1971, at 17, he was sentenced to five years in the Kentucky State Prison, known as "The Castle." While imprisoned, Gray started powerlifting, got many tattoos, and embraced white supremacy.

He was released in 1975 and moved to Denver at his brother's urging. Later that summer, he and a friend were involved in an incident where they fired at a police officer investigating a murder. The officer survived and identified Gray's friend as the shooter, leading to a lighter sentence for Gray. However, ballistic tests linked him to the murder of Joseph Didier, although he was never charged for that crime.

In December 1977, an inmate named David Cook was found dead in his cell, and witnesses pointed to Gray as a suspect. However, witnesses later changed their stories, and Gray was never charged. In 1978, after an early release, he met Sheila Olsbrook, and they had a son. Their relationship included physical abuse, which ended when Gray was arrested again for car theft in 1979. In 1980, he escaped from prison and killed fellow inmate Jerry Keller during a fight.

Gray soon made his way back to Denver, where he was rearrested after a bloody escape. Despite suspicions he had killed another escapee, William Purdue, those claims were never substantiated. In 1982, he met Joleen Sue Gardner, whom he killed after she refused his advances. Convicted in 1984, he was sentenced to 16 years.

After some incidents in prison, Gray was released on parole in January 1991 but quickly violated his parole conditions by traveling to Kentucky. Following his return to Colorado, he was arrested for burglary in 1992. Due to his previous crimes and parole violation, he received a life sentence.

In prison, he committed violent acts against fellow inmates, including murder and sexual assault. By 2000, Gray started confessing to murders he had not been accused of, claiming responsibility for many over his life. He stated that his first murder was in 1971, which he attributed to a prolonged desire for control over his relationships. He talked about murders in multiple states and claimed responsibility for several disappearances.

An investigation into his confessions revealed inconsistencies and doubts about their validity. Although some details seemed accurate, the FBI found many of his claims unreliable. Despite this, he remained a focus of attention due to his violent past. Gray died in prison on July 19, 2013, from heart failure, leaving many details of his alleged crimes uncertain.