"Ishikawa Goemon is considered to be the greatest thief in Japanese history. Goemon was probably a Ninja, since many sources claim that he was born in the Iga Province, the home of the Ninjas. Yet, he perverted ninjitsu in the sense that he used the Ninja techniques to steal from others. Other sources claim that he was a samurai born to So Sekei, the chief retainer of a local warlord. He quit being a samurai after the assassination of his father and became a thief in Kyoto."

Source: www.wayofninja.com