Leonidas Vargas, a once powerful Colombian drug trafficker, has been shot dead in his hospital bed in the Spanish capital, Madrid.
Police said that a gunman entered his room and fired four shots at Vargas, who was being treated for lung disease.
Vargas, 59, was the head of the Caqueta cartel which ran vast cocaine laboratories in Colombia in the 1980s.
After serving a prison sentence in Colombia, he was arrested in Spain in 2006 and was on bail awaiting trial.
The Spanish authorities stopped him for carrying a fake Venezuelan passport, and he was later charged in connection with a 500kg (1,100lb) cocaine haul.
His trial was delayed and he was admitted to the Doce de Octubre hospital for treatment in early January.
Witnesses say two people entered Vargas' room on the fifth floor of the hospital. One man took out a pistol with a silencer and fired four shots at Vargas, who was asleep.
His killing is believed to be part of a settling of accounts between rival drug-trafficking organisations, says the BBC's Jeremy McDermott in Colombia.
Vargas assumed a low profile after being released in Colombia, but in the 1980s he was allied with the powerful Medellin drug cartel of Pablo Escobar.
An idea of the scale of his wealth at the time was revealed after the Colombian state seized $29m worth of properties from him.