Ninja

The mysterious ninja. Walking on water, vanishing into thin air, flying over rooftops...these all have become staples in a Hollywood ninja's fighting repertoire. "What were the ninjas really like," one may ask. "Could they really do all of these amazing feats?"
The ninja are thought to have origninated in 14th century Japan, although there early hisory is hard to know, as there aren't really any written records. One speculation as to why not much is known of the ninja is that many of them may have been taken from humble beginning, and thus were not very literate. Another is that they were just very good at keeping secrets, so not much got out about them.
There had pretty much always been espionage and underhanded tactics in Japan, although it was frowned upon and thought of as not honourable, but there was no specialised training for these spies until around the 15th century, thus the ninja was born. Ninjas were pretty much merceneraies who were just willing to do the kind of things Samurai wouldn't.
The ninjas' primary jobs were espionage, sabotage, and assassination. Ninjas would use disguise so that they could gather information about enemy terrain, installations, and passwords/communiques. Ninja sabotage mostly involved fire...burning castles and camps was common. So far as assassination goes, its always hard to prove that ninjas did it...because they're ninjas! But we all know they did.
Of course, the Samurai and other important people who feared the ninja tried to set up protective measures against them. Passages in castles would often be labyrinthine, so as to make for difficult and long navigation. Gravel, and metal hinges which would squeak, also made for a good early warning system. Segregated building helped to prevent the chance of fire spreading.
Ninjas trained in what is today called ninjiutsu. Although today seen as a type of martial art, taditional ninjiutsu was about espionage and survival skills. Like samurai, the ninja were trained from childhood, and techniques were passed down through generations of family. They were taught martial arts, of course, as well as information about disguise, poison, explosives, and stealth.