Nemesio Rubén Oseguera Cervantes, also known as "El Mencho," was arrested and deported from the U.S. multiple times decades before he became Mexico's most-wanted drug cartel leader.

Cervantes' criminal activity dates back to when he was just 19 years old on the streets of San Francisco, according to a 2019 report by The Courier Journal that cited court records and interviews with both U.S. and Mexican officials. 

The San Francisco Police Department arrested Cervantes in 1986 for trying to sell crystal meth. That's when he was deported the first time. Three years later, Cervantes was back in the U.S. and arrested again, leading to a second deportation.

In 1992, Cervantes and his brother were arrested for selling heroin to undercover officers and landed in federal prison. After a few years, he was out and deported once again, the Courier Journal reported.

Mencho then worked his way up in the Milenio cartel after a brief stint working for the Mexican State Police, according to a his killing at the hands of Mexican police this weekend. He had a $15 million bounty on his head at the time of his death, according to the State Department.

The operation, carried out by Mexican forces with U.S. intelligence support, underscores deepening coordination between the two governments as fentanyl trafficking remains a central political and security issue in the United States.

U.S. authorities steadily increased the reward for information leading to his capture, at one point offering up to $15 million, placing him among the most wanted fugitives globally.

Former DEA official Paul Craine once described Oseguera as "public enemy No. 1" and said he commanded an "army of thousands."

Authorities have linked him to coordinated attacks on Mexican security forces, including a 2015 assault in Jalisco in which cartel gunmen used rocket-propelled grenades to bring down a military helicopter.

Over time, CJNG gained a reputation for projecting strength through public displays of force and social media messaging, reinforcing its position as one of Mexico’s most feared criminal organizations.

Fox News' Greg Wehner contributed to this report.