Gym Leader

Gym Leaders (ジムリーダー Gym Leader) 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 skill of the trainers that challenge them. Every Gym Leader holds a unique badge for the trainers that prove their skill 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.

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 (this is usually more the case in the Anime series rather than the game series). When at the Gym, a leader will maintain the Gym itself, the Pokémon, the other members, and battle any challengers.

Orange Islands
The Gym Leaders from the Orange Islands have only appeared in the Pokémon Anime series and not in game series. In addition to this, these Gym Leaders work slightly differently than others, usually having trainers that face them take part in a number of challenges rather than Pokémon Battles. Also, the majority of these Gym Leaders do not specialize in a specific Pokémon type.