There were several other groups of warriors throughout the course of Japanese history, although the samurai class constituted
society’s elite.
THE NINJA
There are many myths about the Japanese ninja. The ninja historically appeared around the 15th century during the Ashikaga Shogunate, as a group specializing in assassination, guerrilla warfare and sabotage. They were most often exploited by various daimyo for both political and military purposes.
The designation Ninja and Shinobi:
Both ninja and shinobi are written with the same kanji characters and basically have the same meaning.
Use of the word ninja is quite modern. It is ninja that has been popularized as a concept, probably due to some manga series that appeared after the Second World War. A historically more used term than ninja was Shinobi no Mono. In fact, the original name of these warriors was ”Shinobi” or ”Kunoichi” for women. The two kanji characters can be pronounced in two ways: in kun’yomi and on’yomi.
In kun’yomi reading, the Japanese pronunciation, it becomes shinobi-no-mono.
In on’yomi reading, the Sino-Japanese pronunciation of the Chinese characters, it becomes nin-sha, but due to rendaku rules change –sha to –ja.
Both shinobi no mono and ninja primarily have two meanings. It can mean ”person who endures” or ”hidden person” (sneaking person).
Origin:
According to uncertain historical sources, shinobi were descended from Yamabushi. However, they probably originated from the Iga and Koga regions. There are several theories about their actual origin. The earliest traces of ninja can be traced back to about the year 1150, at the end of the Heian period. They were probably of Chinese origin and took refuge in the mountains of Iga and Koga where they lived together with the Yamabushi. They likely received some martial arts influences from Yamabushi monks. Shinobi lived up in the mountains in large clans, with a type of rank order. The fighting tradition was kept within the clan. During the Sengoku Jidai (the era of the great civil wars), Iga and Koga developed into Japan’s major shinobi regions. Just as with the samurai, one was born into the shinobi tradition with training that started as early as childhood.
Some common myths:

The myth of the ninja in black:
The black clad ninja is a myth and it is somewhat unclear where it comes from. There wasn’t some kind of black ”ninja uniform, ninja gi”. There is no evidence for this.
The shinobi were dressed in navy blue peasant clothes, a color also thought could scare away vipers. Shinobi out on a mission, appeared in disguise, such as samurai, priests, artists, craftsmen, ronin, monks.
The popularized black-clad ninja most likely originates from the kabuki theater.
Ninjato, the straight ninja sword:
There is no historical evidence that any ninjato ever existed. The first published image of a ninjato is from the year 1956 in a compendium published by Heishichirō Okuse.
At this time, during the heyday of the shinobi, there was already an excellent weapon, the katana. It was also used by shinobi, who sometimes carried it on their backs.