Hanzo
"
Hattori Hanzo is probably the
most famous ninja of all. He was a vassal and samurai in the service of Tokugawa Ieyasu, and was a major driving force in Ieyasu becoming the shogun and ruler of all Japan. Growing up in Inga, Hanzo first distinguished himself in battles throughout the 1570s. His most famous act came in 1582: When Oda Nobunaga was killed following the betrayal by one of his vassals, Akechi Mitsuhide, Tokugawa Ieyasu was suddenly thrust into a highly dangerous position in close proximity to Mitsuhide. To facilitate Ieyasu’s passage through the Iga province to the safety of the Mikawa province, Hanzo brought together his fellow Iga ninjas—along with their former rivals, the Koga clan—to
escort Ieyasu to safety.
There are also some sources that say that Hanzo helped rescue Ieyasu’s captured family. A master spear-fighter and tactician, Hanzo served the Tokugawas loyally all of his life. Under his leadership, the Iga ninjas became the palace guard of the Tokugawa shogunate at Edo castle, eventually becoming the shogunate’s covert agency under the name Oniwabanshu. After Hanzo’s death in 1596, his successor would take the name “Hattori Hanzo” for himself, a practice which became a tradition of the Iga leaders and perpetuated a myth that Hattori Hanzo was immortal."
And there's the story

so if people ask about the nick you got a cool story to tell, not just "uhhh.. it fits..."