A ninja (忍者, literal meaning: "stealth person") is a warrior and assassin, trained in the Japanese art of Ninjutsu (roughly art of stealth). Ninja, like Bushido and Samurai, followed their own special code of honor called Ninpo and contrary to popular belief the Ninja's specialty was not assassination but rather espionage.

There are many myths and legends concerning ninjas, who were most prevalent during Japan's feudal era and often served damiyos, or feudal lords, for secret missions. Ninjas were never known to wear any color other than black or dark blue despite such western depictions of "white" ninjas which would severely hamper their effectiveness as they conducted most of their business in the dark of night.

Their special abilities are also often exaggerated, such as becoming invisible, turning into animals, jumping over buildings, and the ability to fly and foresee the future. Many of these claims were made by the ninja themselves, others were added by story-tellers and the film industry. (The truth: These myths came about after people witnessed the "Ninja's" feats, the "Ninja" they witnessed were usually Yamabushi that would visit towns performing tricks for money.) In western popular culture, ninjas often depicted as simply supremely well trained martial artists who use many kinds of exotic equipment and skills to achieve their missions. This combined with the popular image of legendary costume of an all black suit and hood leaves only the eye area of the face exposed, often makes up the western take on the ninja as a popular foe of fictional spies (especially on missions in Pacific Asia), superheroes and supervillains.

The ninjas used several special weapons against their enemies, the shuriken and nanchyaku probably being the most famous. Weapons could also be used cleverly as tools such as using the cord of their sword scabbard to construct a hammock between tree branches.

The first major appearance of the Ninja in Western popular culture is in the James Bond film, You Only Live Twice in which the Japanese Secret Service employs a top secret Ninja force to play a critical role in helping the British spy stop S.P.E.C.T.R.E's grandest scheme. Sho Kosugi was famous for his portrayals of ninja in several movies of varying quality.

Comic books have used ninjas extensively since the 1980s with various examples:

  • Although creators Bob Kane and Bill Finger were not aware of ninjas, their creation, Batman has many elements of the type such as his dark colored caped costume, his mastery of martial arts and stealth and his variety of tools he carries in his utility belt.
  • In the Marvel Universe, the most popular ninja character is Elektra. The ninja clan that taught her, The Hand, is also a regular foe of superheroes like Daredevil and Wolverine.
  • Teenage Mutant Ninja Turtles is a parody of Frank Miller's Daredevil stories which include a parody of The Hand, known as The Foot.
  • In Usagi Yojimbo there are several ninja clans, including the Neko who operate in the regular manner, the Komori, who are bats and attack from the air, and the Mogura, moles which attack from below the ground.
  • Ninjas appear also in Lone Wolf and Cub.
  • The GI Joe toy, TV and comic book franchise has ninja characters, especially the popular Snake-Eyes and his COBRA counterpart, Storm Shadow.

In Internet subculture, ninjas are exalted as the focus of a popular, often parodied website, Real Ultimate Power. People who identify with this movement usually extend similar treatment topirates and sometimes lumberjacks