A Ninja Boy (Japanese: ニンジャごっこMake-believe Ninja) is a type of Pokémon Trainer that first debuted in the Generation III games. They appear as little boys dressed as ninjas. They conceal themselves in the landscape and ambush passing Trainers.
Hoenn Ninja Boys have Asian name derivations, while Sinnoh Ninja Boys have European names. The same thing happens to Black Belts.
The way the Generation IV Ninja Boys hold their Poké Balls may be a reference to the popular anime series, Naruto. The titular character's signature move, the Rasengan, is a sphere of energy held in the same way while it is being formed.