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: