Ringleader (noun)

1. A person who leads or organizes a group of people, especially in a criminal or illegal activity.
2. A person who is considered to be the most important or influential person in a group or organization.

Origin:

Ring + leader, from the leader of a group or gang of people.

Examples:

1. The police arrested the ringleader of the gang.
2. He was the ringleader of the mutiny on the ship.
3. The ringleader of the protesters was arrested for inciting violence.
4. She was the ringleader of the group that planned the bank robbery.
5. He was the ringleader of the company, making all the major decisions.