Nicknamed "the Beast" for his reputation as a killer, Salvatore "Toto" Riina was now serving over two dozen life sentences, including one for ordering the assassinations of anti-Mafia judges Giovanni Falconi and Paolo Borsellino in 1992.
The former chief of the mafia organization Cosa Nostra and the so-called "boss of the bosses" Totò Riina died at 88.
Riina's family had been given permission by Italy's health ministry on Thursday for a rare visit to say goodbye.
Riina had been in a medically induced coma for five days, after his health deteriorated following two recent surgeries.
Mr. Riina, one of Sicily's most notorious Mafia bosses, directed the mob's criminal empire during 23 years in hiding.
Riina, who was nicknamed "The Beast" or "The Boss of Bosses", was considered Sicily's most violent Mafia boss.
Rival bosses were mowed down in the 1970s and early 1980s in Palermo as he orchestrated his rise to power.
In the autumn of 2017, it was reported that the then leader of the Cosa Nostra had ordered to his son to kill his own sister because she was dating a policeman.
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The archbishop of Monreale, which includes Corleone, said Friday that Mr. Riina's death "ends the delusion of the Cosa Nostra boss of bosses' omnipotence".
He notoriously ordered the murder of a 13-year old boy who was kidnapped in an attempt to stop his father from spilling mafia secrets.
He was behind a series of mafia bombing in Rome, Milan and Florence in 1993, which left 10 people dead. Pictures of the defendants during trial were not allowed by the Court.
Two anti-mafia judges, Giovanni Falcone and Paolo Borsellino, were also killed by auto bombs in 1992 under Riina's command. He was imprisoned under a law - known as the 41-bis - that imposes strict security for top mobsters, including isolation in prison and limited time outside their cells.
Riina is thought to have ordered over 150 murders until his arrest in 1993 from a Palermo apartment six months after Borsellino and his police escorts were killed by a vehicle bomb.
However, the request had been denied, and he died in prison hospital.
A native of Corleone, a Sicilian hill and Mafia stronghold, he steadfastly refused to collaborate with law enforcement after his capture. He had been caught on a wiretap this year saying he "regrets nothing ..."