ringleader; mastermind; leader of a plot
Refers to the person who instigates or leads a conspiracy, rebellion, or criminal scheme. Often used in historical or dramatic contexts.
A less common, somewhat literary use for someone who leads the way in a field or movement. Often replaced by 先駆者 or パイオニア in modern speech.
The ringleader of the incident has not been caught yet.
He is known as the mastermind of the coup.
He is sometimes called a pioneer of modern medicine.
Composed of 首 (head, chief) and 魁 (leader, pioneer). The exact historical derivation is uncertain, but the combination naturally conveys the idea of a leading figure.