Danzo Shimura was once a shinobi who worked for Konohagakure. After being killed by Sasuke Uchiha, he wasn't heard from again. Once Madara Uchiha was revived, he used a life restoring technique to bring Danzo back to life. After trying to recruit Danzo, Madara forced Black Zetsu to merge on one side of him, enhancing his powers.