key figure

n. an important person in an event; a person central to an event. Sam is not exactly a key figure, but he can lead us to Mr. Big.

Name	Pronounced	Usage
Appius	AP-pi-uws (Ancient Roman), AP-ee-əs (English)	Ancient Roman
Steve	STEEV	English
JÓRunnr	-	Ancient Scandinavian
Kalani	-	Hawaiian
ÉRiu	-	Irish Mythology
Eustorgius	-	Ancient Greek (Latinized)