Jhon Jairo Velásquez Vásquez, alias "Popeye," who worked for Colombian drug lord Pablo Escobar has succumbed to stomach cancer on Thursday, according to an article by the BBC. He was 57.

Colombia's National Penitentiary and Prison Institute (INPEC) confirmed through a Twitter post the death of Escobar's top hitman, who was hospitalized over a month ago.

Velasquez had been admitted to the hospital since December 31. A local media outlet reported he was battling the disease for several months and was undergoing chemotherapy at the National Cancer Institute in Bogotá.

Velasquez who commanded the drug kingpin's army of hitmen, confessed to 300 assassinations and claimed he coordinated thousands as part of the infamous Medellin Cartel that sent thousands of tons of cocaine to the United States.

The Medellin Cartel made his boss one of the world's richest men during the 1980s and 1990s. Escobar was killed by Colombian police in 1993 as he attempted to avoid extradition to the US.

In 1992, the former hitman gave himself up to authorities and was sentenced to 30 years in prison for the assassination of presidential candidate Luis Carlos Galan in 1989 and reportedly gained a reputation for the stories he told about his life of crime. After serving most of his sentence, more than 20 years, he was released in 2014.

He launched a YouTube channel called "Repentant" and eventually became a popular online personality, attracting more than a million followers. He said he used the platform to show his reincorporation into society.

Velasquez then went into hiding for several years fearing reprisals from his victim's families and members of the Medellin Cartel he helped to convict in return for a lighter sentence. However, he was captured again on May 25, 2018 on charges of extortion and criminal conspiracy and was taken into custody at a party hosted by Colombia's top drugs trafficking investigator.

Mayor Federico Gutiérrez of Medellin confirmed the arrest in a tweet.

Local media outlets reported that Popeye was arrested after appearing with his lawyer at the organized crime prosecutors' office in Medellin in hopes of finding out if he was being investigated.

A source within the Oficina de Envigado, the collection of Medellín crime groups that controls most of the city's underworld, said in an interview with InSight Crime last year that Popeye was blackmailing frontmen for his late boss who had held on to assets linked to the Medellín Cartel's illegal activities.

"He was trying to recover property [and] money that he left years ago in the hands of narcos, and that very likely was inherited or received by their relatives, who are the ones who have been pressing and are the ones who denounced him," a source told El Tiempo.

The same source added that the US Immigration and Customs Enforcement (ICE) agency participated in the investigation.

The life of Velasquez was the subject of television series, including Netflix's "Narcos" and "Surviving Escobar" which was based on a book he authored.