A ringleader is the person who organizes and leads others in an activity, especially one that's mischievous, rebellious, or against the rules. When a group of students decides to coordinate a cafeteria food fight, someone usually comes up with the plan and gets everyone else on board: that person is the ringleader.

Today we usually use this word for someone who leads others into trouble or orchestrates something bold. If five kids sneak out during recess but one of them planned the whole escape and convinced the others to join, that child is the ringleader.

A ringleader is the organizer, the one who gets the ball rolling and persuades others to follow. They take initiative and bring others into their plan. Teachers often try to identify the ringleader of a disruption because they know that once you address the person who started it, the others typically settle down. In serious contexts, police might arrest the ringleader of a criminal gang, meaning the person who planned and directed the operation. The word suggests both leadership ability and questionable judgment about how to use it.