Board Thread:Naruto Discussions/@comment-24422163-20140702214928/@comment-1512913-20140703101355

We know all of Kakuzu's backstory. "When under the servitude of Takigakure as an elite ninja, Kakuzu took on a mission to assassinate Hashirama Senju, the First Hokage. This mission, however, ended in failure against the mighty ninja. Despite the insurmountable danger faced on the mission, what awaited his return to his village was the stigma and harsh punishment associated with the failure of his objective. In response to this treatment, a wrong levied against a shinobi who had put life and limb on the line for his village, Kakuzu came to hold a violent hatred for Takigakure as he escaped from imprisonment. In his flight from the village, Kakuzu killed the village elders, took their hearts, and fled with knowledge of the village's most prized forbidden techniques. He made a living off bounty hunting on the black market, and tearing out the still-beating hearts of powerful shinobi to extend his own lifespan and arsenal"

For Hidan: "After Yugakure deteriorated from a shinobi village to a tourist site, Hidan became infuriated with how things were turning out. He believed that the shinobi that resided there were meant to kill, and thus slaughtered his neighbours before leaving Yugakure, and joining the cult-like faith known as Jashin, a religion that worshipped a deity of the same name. The primary teaching of this faith appears to be outright slaughter, where anything less than utter destruction is considered a sin. Through experiments with Jashin's secret technique, Hidan was granted immortality"