There are many versions of his story and many mysteries surround him. According to the legend he practiced sorcery, performing amazing feats such as swallowing a bull in front of the crowd of over 20 people; his alias comes from his alleged ability to fly. Today, researchers believe his supposed magical arts were illusion as a type of group hypnosis. However, this belief has never been proven to be the case and therefore is only considered to be a possibility. His date of birth and death are unknown.
According to historical documents, the daimyo Uesugi Kenshin had heard of Danzō's reputation, which had led for him to invite Danzō to his prime castle. Kenshin decided to test Danzō's abilities by challenging him to sneak into a certain castle and to retrieve a prized naginata (a sword in another version of this story) from one of his retainers, Naoe Kanetsugu. Danzō infiltrated Kanetsugu's heavily guarded castle and not only succeeding in stealing the naginata, but also captured a young servant girl. Kenshin then realized that Danzō would be a very useful ally and took him into his service. However, Kanetsugu plotted to kill Danzō (according to another version it was Kenshin himself who ordered his death, perceiving him to be too skillful and thus dangerous), forcing him to try to defect to Takeda Shingen, Kenshin's rival. Suspecting Danzō to be a double agent, Shingen however ordered him to be killed. Danzō was captured by Takeda men and executed through decapitation.
In popular culture
Katō Danzō makes a prominent appearance in the manga series Path of the Assassin, where he is known as Kite Katō, a fearsome shugenja and nearly unrivaled shinobi. He also appears in a minor role in the video game Samurai Warriors 2 as a fire ninja bodyguard. In the manga and anime series Naruto, there is a character with the name "Danzō" who leads a secretive covert ops team ROOT and another character called Dan has the surname "Katō".