kingpin

The innermost or central pin in an arrangement of bowling pins.

The most important person or element in an enterprise or system.

The axis around which steered wheels pivot; a bolt that holds the axis in place—a kingbolt.

The pin at the centre of the triangle of bowling pins (originally the tallest pin in kayles). Sometimes also the headpin at the apex.

The most important person in an undertaking or organization.

The bolt holding together the truck of a roller skate or skateboard.

the most important person in a group or undertaking