Ninja was a covert agent or mercenary between 12th–19th centuries (Kamakura– Edo period). Ninja received training for so-called ninjutsu techniques, accomplished a secret action. They wore dark blue or purple garb (shinobi shōzoku).
The Iga (modern Iga City, Mie Prefecture) and Kōga (modern Koka City, Shiga Prefecture) clans are the most famous ninja clans. Because there are many movies, novels and comics about ninja, ninja is famous in the world.