For many people, the first thing they think of when someone says "Japan" is weird porn. The second thing is generally ninja. However, unbeknownst to you, their greatest trick of all is fooling people into thinking they existed in the first place.
Just to start off, I am going to say that if you believe there was a real group of people called ninja (or shinobi, as you will be corrected by nerds whose knowledge of several Japanese words places them several rungs above you in life), you are basically on the same boat as people that believe 9/11 was orchestrated by the Zionist illuminati lizard-men conspiracy. You do not know this yet, because our culture as a whole has wanted so bad for something this awesome to exist.
Let's step back and look at where the ninja myths are coming from. The primary period of 'ninja activity' is the Age of the Country at War, which runs from around the Onin War of 1467 until the establishment of the Tokugawa Shogunate in the early 1600s. The cental authority had broken down, and local samurai bigshots basically grabbed whatever land they could and started fighting against their neighbors to get more. It was like the Wild West, Medieval Europe, and SAMURAI SWORDS all rolled into one. It was basically the sweetest thing ever. Novelists, video game writers, and teenage boys the world over agree without question. In this period, there were indeed assassinations going down, but the important distinction to be made, that many a ninja fan will agree with me on, is that a dude killing another dude by cover of night doesn't make him a ninja. It basically just makes him a jerk. Legends did run wild at the time, true, of 'men of the shadows.' This is less to do with the existance on ninja and more the talk of guards who didn't want to admit they were playing their Nintendo Abacus 5 while a dude strolled in and popped a pre-modern Japanese cap all up in their lord.
goddamn ninja man, know what I'm sayin?
Tokugawa Ieyasu eventually calmed things down and brought the country under control, and Japan entered a period of peace and mass consumption of plays and books, leading to many a tale of a gallant samurai and of the magical ninja (I swear man I was here guarding the whole time he must have been able to teleport or some shit. Maybe turn into a frog I dunno). This started a trend: the one thing that ninja do best is not stealth or assassination, but making cash money.
This only acceletared in the modern age; after world war II, there was another fluorishing of peacetime culture as well as of the desire to make a quick buck. Two provinces in the Kinai region of Japan rediscovered their proud ninja heritage and will very gladly give you exact directions to the hidden mystical ancient giftshops nestled in the hills. There is even a ninja restaurant in Kyoto. As if this wasn't enough, sometime in the 70s, a man 'rediscovered ninjutsu,' the secret hidden art of the ninja that had supposedly been super seriously guys pased down in his family that he suddenly remembered so he could open ninja schools. Soon enough, franchises opened in America, where now you not only have pricks-who-know-three-words-of-Japanese, but the some of very same who also believe they are ninja.
Heir to a long and proud tradition
The Wikipedia page on ninja is one example of just how bad the desire for ninja to exist can get. There are over 100 citations- oh jeez wait! Something with that many citations can't be wrong! I have written this article in error.
By the by, I have a mile-long wang (me, 2009) and I regularly bed over 9000 women daily (me, 2008). I am also the nicest and smartest boy in the world (my mother and your mother, et al. 2005). Do you see what I have done just there? A citation does not mean anything past the simple fact that someone else agrees with your opinion. If it is a book, it simply means they have additionally managed to run it past an editor who may or may not have any background in the topic himself. One must observe just where the citation leads in order for it to have any merit.
There is simply no evidence that any of what formed "the ninja" today is rooted in anything more than the desire to tell a sweet story and make a quick buck. This desire relating specifically to Our Masked Friends has been around since the Edo period, but a historical lie is still a lie. Things don't change when these lies are repackaged, given full-color illustrations, and published under Osprey Publishing (a fine company whose authors account for 80% of the citations in the Wikipedia article that aren't about simple historical facts, the other 20% being from schools of Ninjutsu which have no incentive to mystify or legitimatize themselves whatsoever).
And there you have it. The Ninja is a lie. You can tell the ass complaining about how Ninja Gaiden isn't historically accurate that it does about as well as anything about ninja, because they are totally fictional. What's that I hear your thin, tremulous nerd voices calling in between mouth-drawn breaths? "Of course there are no concrete records of the Ninja, you cretin! They were masters of secrecy!" Why does that sound familiar? Oh right, because it is the same reason that there is no evidence that the Free Mason Society of Gay Agenda Wizards have been hoaxing us into believing that the moon exists so their tide-generating baby consuming machines can continue to churn their infernal blades without hinderance.
HAHAHA! Yesssss! Churn, churn!