Phillip Dean Hancock was born on February 15, 1964, in Oklahoma City. He was the older of two sons. Phillip had a younger brother who was diagnosed with cerebral palsy after being born with the umbilical cord wrapped around his neck. As they grew up, Phillip took on the role of protector for his brother. He looked after him and even fought older boys to stop them from bullying his younger brother.

As a child, Phillip's family attended a Methodist church. However, he often spent time at nearby car salvage lots where he smoked marijuana and cigarettes with other kids. Phillip's home life was difficult. His father was known to be abusive to both his children and his wife. This situation became so severe that Phillip's mother once had to leave home to escape the violence.

On May 26, 1982, Phillip Dean Hancock killed his first victim, Charles Lester Warren, in a park in Oklahoma City. Hancock and his accomplice, Kenneth Ray Hulsey, were involved in a shooting incident. Warren, who was 27 years old, was considered to be a drug dealer. Before the shooting, there had been verbal altercations between Hancock and Warren over a missing ring. Witness Patrick Michael O’Brien later testified that he saw Hancock being beaten by Warren. Hancock claimed that Warren threatened him. Feeling fearful for his life, Hancock took Hulsey's rifle and shot Warren multiple times, resulting in Warren's death. During the ensuing chaos, two bystanders were also injured.

Hancock surrendered the day after the incident and was charged with murder and other offenses. His trial began in October 1982 and ended with a conviction for first-degree manslaughter. The jury accepted Hancock's claim of self-defense, and he was sentenced to four years in prison. He served less than three years before being released on parole.

Nineteen years later, on April 27, 2001, Hancock murdered two men, Robert Lee Jett Jr. and James Vincent Lynch III. That night, Hancock went to Jett’s house, where a dispute over cigarettes erupted into violence. Jett reportedly pulled a gun, and during a struggle, Hancock shot both Jett and Lynch. One witness, Shawn Tarp, recalled that Hancock chased Jett into the backyard and shot him while Jett was on the ground, stating he would die. Neighbors called the police after hearing gunshots.

Despite a police sketch, Hancock evaded arrest for about a year until he was eventually caught for drug and firearm-related crimes. Following forensic evidence linking him to the earlier murders, he was charged with two counts of first-degree murder. Hancock claimed self-defense during his trial, but the jury found him guilty. He was sentenced to death in 2004.

Hancock remained on death row for 19 years. His appeals were denied, and he filed various motions, including requests for DNA testing related to his claims of self-defense. In 2023, a clemency hearing recommended converting his death sentence to life without parole, but the governor ultimately denied this request.

On November 30, 2023, Hancock was executed by lethal injection. He maintained his innocence and insisted that the murders were acts of self-defense. Before his death, he criticized the prosecution and expressed gratitude to his legal team. For his last meal, he requested fried chicken and root beer.