A mob boss (Italian: Don) is the head of an organized crime syndicate, who is the leader of a crime family. In the Sicilian Mafia, they are known as a "Don", in the Triad they are known as the "Mountain Master", while in the Yakuza, they are known as a Kumicho.
In organized crime, every single crime syndicate has a figurehead, a captain, to rule them. The boss of a family is typically a wealthy and powerful man, like a king. A boss chooses a successor, whether it is in his blood family or in his ranks. A boss gives directions to his underboss(es), who in turn sees that the Capos oversee that the soldiers or buttonmen accomplish the task. The boss of a family lives in a family's compound, which is generally a fortress-like mansion guarded by hired guns, and family (sometimes, even made men) sleep, eat, and live there. Bosses are advised by a consigliere (Deputy Mountain Master) in their actions=
Bosses try not to be up close in fighting, sending their made-men to carry out the bloodshed instead. However, Trapani crime family bosses Aldo Trapani and Dominic were very active, killing over a thousand mobsters. In 1932, Costillo crime family boss Tony Camonte carried out the Camonte-O'Hara War personally, using Tommy Guns to gun down several of the Chicago North Side O'Hara Gang members, including Charley O'Hara and Joe Gaffney.
Some powerful Sicilian bosses get seats on The Commission, the legislature of the Mafia. Bosses represent their families in meetings to discuss important matters, such as the Five Families War, the retirement of Hyman Roth, and the retirement of Michael Corleone. They give permission to put hits out on people, including the bosses or made men; otherwise it is infamia.