Gym Leaders are the highest ranking member and owner of an official Pokémon Gym. A Gym Leader will usually specialize in one specific type of Pokémon, and uses them to test the skills of trainers that challenge them. Every Gym Leader holds a unique badge for the trainers that prove their skills to them or defeat them in battle. When a trainer has a total of eight badges, they can compete in their regional League or challenge their region's Elite Four. There are a total of eight Gym Leaders in each region.
As shown several times, a Gym Leader is usually well involved with their community. When not at the Gym, a Gym Leader is usually involved in some type of work or service that the surrounding community is known for. When at the Gym, a leader will maintain the Gym itself, the Pokémon, the other members, and battle any challengers.