Every group needs a leader to organise things and generally be in charge. This page lists the characters who act as the heads of Clubs or School Committees.
Note that it is generally perfectly acceptable for someone to be both the head of a club as well as a member of a committee, as long as it doesn't interfere with their duties. Mutsumi Mitsuba, for example, is the Judo Club captain, but also a member of the Swim Meet Planning Committee. Nene Todorki is head of the Robot Research Club as well as a member of the Library Committee, while Kaede Igarashi is head of both the Disciplinary Committee and the Chorus Club.