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.
The ringleader of the incident has not been caught yet.
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.
He is known as the mastermind of the coup.
He is sometimes called a pioneer of modern medicine.