Kingpin \KING-pin\ , noun;
1. The person of chief importance in a corporation, movement, undertaking, etc.
Between a Rolling Stone article about a Texas-born drug lord, a Playboy article about a big female Meth dealer, and the Breaking Bad marathon my husband and I have been watching, kingpin has been popping up quite a bit lately. In fact, with the decades-long drug US drug war this word seems to be relatively common, which is why I was surprised at the dearth of information about the word in the Oxford English Dictionary. The OED offers no etymology and lists just two definitions:
1. The tallest (central) pin in the game of kayles
2. That which holds together any complex system or arrangement; also, the most important or outstanding person in a party, organization, etc.
Other sources list a couple more definition, notably the bowling one ("the headpin" or "the #5 pin") and a mechanical definition ("either of the pins that are part of the mechanism for turning the front wheels in some automotive steering systems").
The oldest usage of this word dates to 1801 and it's the first OED definition listed above. It's a combination of king (as in "chief, main") and pin (referring to the pins used in the game). I'd guess that the fact that a kingpin is the tallest and most central pin in this game leads pretty directly into the other definitions. So, if the most central and noteworthy person in an organization is the one running things, he or she is therefore the kingpin.