Hanzō is a villain in the Naruto series, most likely serving as the main villain of Nagato's backstory, and he was the leader of the Hidden Rain Village before he was overthrown and murdered by Pain. He was later reanimated by Kabuto Yakushi during the Fourth Great Ninja War.
As a child, Hanzo was implanted with the poison sac of a black salamander that died in his village. The surgery intended to create a ninja able to poison others and immune to all forms of toxin, Hanzo was required him to wear a mask to protect others from his venom-laced breath. In his youth, defeating Mifune in the past but spared his life, Hanzo once sought the ideals of "peace" and even attempted to achieve it with the unification of the Five Great Countries. However, after realising that such a method would only bring about perpetual war and thus, leave only death in its wake, he cast aside this conviction and focused on maintaining his status as the Hidden Rain Village's ruler.
Hanzo later gave the same respect to the team of Jiraiya, Tsunade, and Orochimaru during the Second Great Ninja War where he christened them the Sannin for enduring his attacks. He also engaged into battle with Chiyo numerous times, allowing her to create an antidote to his salamander's poison. Years later during the Third Great Ninja War, Hanzo feared the budding Akatsuki and its unorthodox means to end conflict as a threat to his regime, requesting the services of Danzo Shimura to eliminate the organization's three top ninja (In an anime filler it was revealed that Danzo secretly manipulated Hanzo into this alliance by framing the Akatsuki for trying to overthrow him). However, though Yahiko died, Hanzo's scheme only caused Nagato, as Pain, to start a civil that ended with Hanzo killed by Nagato through Yahiko's body. Pain did not stop by only killing him but as well as killing his close relatives & ambassadors from other nations as well as considering his name a taboo in Hidden Rain Village under his reign.
Hanzo was among the ninja reanimated by Kabuto for the Fourth Great Ninja War. After being mobilised, he became part of the group that Chūkichi from the Surprise Attack and Diversion Platoon requested assistance from, along with Chiyo and Kimimaro. Encountering the remnants of the Alliance's Surprise Attack Division with this improvised team, Hanzō chastised Deidara for being caught and remarked that he would have had no intention of freeing him, if it weren't for the accursed technique which governed his actions.
Summoning Ibuse, Hanzo overpowered the allied ninja until Mifune arrived. As they engaged in their rematch is defeated by Mifune, Hanzo learns that he loss of conviction in his ideal for peace dulled his skills. After Hanzo reminisced about his past battle with Mifune, where he divulged the details surrounding his infamy eventually spared the defeated samurai due to his strong devotion towards his allies, he then explained that the weakness he described then still remained despite his immortality. In a tremendous demonstration of will, Hanzo places his faith in Mifune and — overcoming the talisman that governed his actions — stabbed himself to pierce his poison sac and leave him paralyzed for the Fifth Division to quickly seal him for the duration of the war until the Reanimation Jutsu was canceled.