Pablo Escobar's Main Hitman 'Popeye' Dead in Colombia from Cancer

Pablo Escobar's trusted hitman -- who confessed to killing more than 300 people -- has died, but not in a hail of bullets ... instead, he lost a battle with stomach cancer.

Jhon Jairo Velásquez Vásquez -- widely known by his alias, Popeye -- died early Thursday at the National Cancer Institute in Bogota where he'd been receiving care. Popeye was hospitalized on New Year's Eve for esophageal cancer, according to prison officials.

He was ultimately transferred to the institute when the prison found out about his cancer diagnosis. Popeye had been behind bars for more than 20 years after confessing to the murders ... the majority of which came at Escobar's orders.

Popeye wrote a book in 2005 about his time in the Medellín Cartel: "Surviving Pablo Escobar: 'Popeye' The Hitman, 23 Years and 3 Months in Prison." He was released from prison in 2014 but was recaptured just 4 years later for a slew of other crimes, including extortion.

The hitman -- who once plotted the assassination of a former Colombian presidential candidate -- gained notoriety on YouTube spewing hate-filled rants and defending conservative political views. He had more than 1 million subscribers on his channel.