Nemesio “El Mencho” Oseguera Cervantes was a feared Mexican drug lord and the leader of a ruthless cartel accused of masterminding efforts to push fentanyl into the United States. Once a police officer, Oseguera went on to become one of the world’s most wanted fugitives, with the United States alone offering a $15 million bounty for information leading to his arrest. Oseguera, who formed and led the Jalisco New Generation Cartel (CJNG), was an elusive figure who had been considered Mexico’s most powerful cartel boss since Sinaloa kingpin Joaquín “El Chapo” Guzmán was arrested last decade. Born in July 1966...