Kakuzu, formerly an elite member of Takigakure, was one of Akatsuki's members.
In the original story, Kakuzu was Hidan's partner. He possessed the secret technique Earth Grudge Fear, which allowed him to manipulate the black tendrils released from his body with chakra and steal other people's hearts.
Including his own heart, he could store up to five hearts within his body. By replacing his hearts, he extended his lifespan and was known as "the man who lived as long as heaven and earth."
Each of those hearts could transform into a black-bodied monster formed from Earth Grudge Fear, and those monsters could use the techniques of their hearts' original owners.
During the First Shinobi World War, Kakuzu had personally witnessed Ginkaku being killed by the Second Hokage and Kinkaku undergoing a Tailed Beast Transformation. After a long time had passed, Kakuzu received an invitation from Pain's Deva Path to join Akatsuki, becoming its financial manager. However, every ninja assigned to carry out missions alongside Kakuzu was killed by him, until he met the immortal Hidan. The two then became known as the Immortal Duo. Though they worked well together, they argued without end.
Kakuzu himself believed that money came first. On several occasions, he even took jobs along the way to earn travel expenses, slightly delaying their journey and earning Hidan's dissatisfaction. As for the five hearts he possessed, each retained the chakra nature of its original owner, while the other hearts provided supporting attacks.
Kakuzu was actually ninety-one years old. However, before his bodily functions ceased, he would seize another person's heart for his own use, allowing him to survive from the era of war to the present.
After receiving their mission, Kakuzu and Hidan defeated Chiriku, one of the Twelve Guardian Ninja of the Fire Temple, as well