A kingpin, also called a "center pin" or a "five pin," is the pin at the very center in bowling. From the bowling pin definition of kingpin, we get its other common meaning: someone who is important. If you are the kingpin in your office, you are probably the boss.
The kingpin is the bigwig or the very most important, authoritative, or essential person in a group. The kingpins of the music business are often the owners of record labels rather than the actual musicians, and the kingpin of your bowling team is the person who bowls a strike every single time. In machines, an important vertical bolt can also be called a kingpin. In other words, there is a good reason that king is the most important part of kingpin.