ringleader

noun

1. A leader of a group of people, especially an unofficial group.

   “Once, on a confident whim, I approached the group of popular girls in an attempt to broaden my circle. Their ringleader took one glance at my new Aeropostale T-shirt and whispered to her clones, “Yeah, Aero's definitely out now.””

2. A person who starts and leads a disturbance (such as a riot), a conspiracy, or a criminal gang.

   “The police arrested the ringleaders of the smuggling operation.”

   “A sort of naughty persons, lewdly bent, / Under the countenance and confederacy / Of Lady Eleanor, the protector's wife, / The ringleader and head of all this rout, / Have practis'd dangerously against your state...”

   “The ringleaders of the gang were eventually hanged at Tyburn.”