Part 1The Origins of the Ninja:
A Ninja, according to Japanese history, was a warrior that had received special training in rather unorthodox arts of war. These lesser used and unusual types of warfare included illusion, assassination, and espionage, and scouting or surveillance.
The origins of the Ninja are shrouded in uncertainty, but it is known that they first appeared in the 14th century, and remained active until the Edo period which ended toward the latter half of the19th century.
The services of a Ninja may have been in the hire of a feudal lord or other faction waging some form of guerilla warfare.
Ninja is derived from the Japanese word "ninjutsu" and roughly translated means people who practice stealth and invisibility. The word ninja became popular after WWII.
According to "The Historical Ninja" By Sôke Masaaki Hatsumi:
"Ninjutsu did not come into being as a specific well defined art in the first place, and many centuries passed before ninjutsu was established as an independent system of knowledge in its own right. Ninjutsu developed as a highly illegal counter culture to the ruling samurai elite, and for this reason alone, the origins of the art were shrouded by centuries of mystery, concealment, and deliberate confusion of history."