From Bulbapedia, the community-driven Pokémon encyclopedia.
is the Head Leader at the time of Ash's journey.
A Head Leader (Japanese: ヘッドリーダー), also known as the Orange Crew Supreme Gym Leader, is the top-ranked Gym Leader in the Orange Crew and serves as the final obstacle in the Orange League. Those who defeat the Head Leader in a Pokémon battle earn the Winner's Trophy, become the League Champion, and are honored in the Palace of Victory. The term "Head Leader" is not used in the English-language dub and Drake is merely implied to be a fifth Gym Leader; the distinction is clear in the original Japanese version.
At the time of Ash's journey in the Orange Islands, the Head Leader is Drake. Ash defeated Drake in Enter The Dragonite. No other Head Leaders have been seen in the anime and it is unknown how one rises to this position.
In battle, the Head Leader must obey specific rules that give an advantage to the challenger. For example, the Head Leader is unable to switch Pokémon mid-battle while his opponent is free to do so at any time.
Although the Head Leader occupies a similar position in the anime to the Champions of the various Elite Four in the video games, he is not displaced upon defeat.