Hanzo Hattori the son of Yasunaga Hattori, was born a vassal of the Tokugawa clan, and served Ieyasu Tokugawa; he would later earn the nickname oni-Hanzo because of the fearless tactics he displayed in his operations.
Hanzo Hattori was born in 1541, the son of Yasunaga Hattori a hereditary of the Tokugawa. Hanzo was a member of the Hattori family, the leaders of the ninja community of Iga Province in feudal Japan. It is thought that there may have been as many as four ninja who took the name Hanzo Hattori. The ninja who made famous the identity of Hanzo Hattori was named Masanari. He was said to have begun training on Mt. Kurama north of Kyoto at the age of eight, and became a full-fledged ninja at age twelve, and was known as a master ninja at the age of eighteen.
He fought his first battle at the age of 16 in the form of a night attack on the castle of Udo in 1557, and went on to serve with distinction at the battles of Anegawa in 1570 and Mikatagahara in 1572, but his most valuable contribution came in 1582, following Nobunaga Oda's death. At that time Tokugawa and his retainers had been staying near Osaka and learned of the assassination only just in time to avoid being detained by Mitsuhide Akechi's troops. But they were by no means out of the woods. Mikawa was still a long way away, and Akechi men would be combing the roads for them. At this point, Hanzo suggested that they take a route through Iga province, as he had ties with the samurai there. In addition, Ieyasu had sheltered survivors from Nobunaga's bloody invasion of that province in 1580 and those who knew of this would certainly be well disposed to offer assistance. Tadakatsu Honda sent Hanzo on ahead, and, as hoped, the Iga men agreed not only to guide them along back roads, but also to provide them with an escort. At length, Tokugawa and his band returned to Mikawa safely.
Ieyasu started to put more Iga ninja in service of Hanzo and together they did underground espionage operations, And in 1590 became gaurds of a gate in Edo Castle from then on that gate was called Hanzo-mon (Hanzo's gate)
Hanzo died in 1596, aged 55, and was succeeded by his son, Masanari Hattori. His men carried on being the gaurds of Edo castle under a less successful leader and the Hanzo gate still bears his name.