kingpin vs important person

kingpin and important person both are nouns.

Word	Noun	Adjective	Verb	Adverb
kingpin	Yes	No	No	No
important person	Yes	No	No	No

As nouns, important person is a hypernym of kingpin; that is, important person is a word with a broader meaning than kingpin:

kingpin: the most important person in a group or undertaking
important person: a person whose actions and opinions strongly influence the course of events

Other hypernyms of kingpin include influential person, personage.

kingpin (noun)	important person (noun)
bolt that provides a steering joint in a motor vehicle	a person whose actions and opinions strongly influence the course of events
the front bowling pin in the triangular arrangement of ten pins
the most important person in a group or undertaking