A boss, kingpin, or crime lord was the individual in charge of a criminal organization.
Among the Iotians of Sigma Iotia II, whose culture was patterned on the Earth book Chicago Mobs of the Twenties, the leaders of the mob organizations or "outfits" were called bosses. Each boss administered a territory, and they collectively operated in lieu of a conventional government. Ordinary people were expected to pay "a percentage", in return for which the boss would take care of their needs.
In 2268, there were "maybe a dozen" bosses on the planet, not counting the "small fry". These included Bela Okmyx of the Northside Territory, Jojo Krako of the Southside Territory, and Tepo. (TOS: "A Piece of the Action")
Sneed was a Ferengi crime lord who operated on M'talas Prime until his death at the hands of Worf in 2401. His associate and "brother", the Vulcan Krinn, was the kingpin of the V'Lashi crime syndicate. (PIC: "Disengage", "Imposters")