Ninja is a special occupation in Japan. Simply put, it is a killer trained by specialized institutions in ancient Japan to perform dangerous and confidential tasks.
The name Ninja was officially used in the Edo period in Japan, but this profession can be added to a longer period. According to Japanese legend, it was the first time that Shoto Kutaishi used Ninja to complete the task in Japan. At that time, the ninja didn't call it that, but it was called "forbearance" alone.
In Asuka's time, ninjas were called "smart". Nara era was called "Scout", and there were many names in the Warring States period, among which "Luan Bo" was the most popular. This is the evolution of the name ninja.
Although the ninja only got an orthodox name in the Jianghu era, it was also because of the beginning of the peaceful period under the rule of the Tokugawa family in that era that the role of the ninja became worse and worse. Finally, the culture including Ninjutsu was gradually lost and forgotten.
In the historical records of Japan, there are indeed records about ninjas. In 1637' s "Shimahara Rebellion", the ninja took part in this battle as a subordinate of the shogunate.
So, when is the most active period of ninja on record? The period from the end of 1 1 to the end of 12, the Southern and Northern Dynasties in 13 century, and the Warring States Period from the middle of 14 century to 15 century was a great period for ninjas to "let a hundred schools of thought contend".
15, 16 century ninjas were still active, and at this time ninjas began to distinguish between upper, middle and lower grades. Ninja costumes and weapons are no different from what we see in movies and TV plays. At the same time, they also created a whole set of spy information technology system, which could shine brilliantly in the Warring States period with the help of superhuman skills.