"El Betito" is linked with multiple murders and is accused of heading up a fearsome Mexico City drug gang.
"El Betito" - the suspected head of Mexico City's Tepito Union gang - was detained in the south west of the sprawling city, said national security commissioner Renato Sales.
He had lost about 4st 10lbs (30kg) through gastric band surgery to reduce the size of his stomach.
Police photos show the 37-year-old looking considerably more slimline, bearded, and with a fuller head of hair.
He was arrested in the Rincón del Pedregal neighborhood carrying $10,000 (£7,825), drugs and a handgun.
He is accused of being the boss of the most notorious drug gang in the Mexican capital and is being investigated over various murders.
The Tepito Union gang is said to be involved in drugs, kidnappings, extortion and weapons, and takes its name from Mexico City's gritty Tepito neighbourhood.