Kakuzu was an S-rank missing-nin from Takigakure and a member ofAkatsuki who was partnered with Hidan. Within the organisation itself, Kakuzu acted as the organisation's Treasurer.
There is not much information on Kakuzu except for the fact that he hated his village because he was imprisoned and shamed for not being able to assassinate Senju Hashirama, the legendary Hokage. Despite the fact that he was unsuccessful but still survived his fight is a testament to his ability as a shinobi. After leaving his village, he became a mercenary that hunted down people to collect bounties on their heads. To ensure he continue to live, Kakuzu would rip out the still beating hearts of powerful shinobi he defeated and implant them into his body using a secret technique.
He was known to follow the path of money. He would take jobs or sometimes go off course in order to do something where he saw monetary gain. He would not bother involving himself if there was not something he could gain.
The only real time we see him in action is when he takes on Kakashi and later on Naruto. While Kakashi is able to destroy one of his hearts, Kakashi is overmatched by Kakuzu's ability to use a variety of element techniques. During his fight with Team Kakashi, Kakuzu decides that he wants to take Kakashi's heart. Kakashi, however, is saved by team Yamato, which now includes Naruto.
Naruto finally finishes off Kakuzu with the first Wind Release: Rasenshuriken he has ever used in combat. The technique was said to be so powerful that when Tsunade examined the body, she said that Kakuzu was damaged at a cellular level.
Frankly, I felt like Kakuzu and Hidan were just throw-in characters that were put in to give us some good fights. They were both strong and had ridiculous powers, but there was no real story to either on. I am not complaining though since they did deliver some great fights haha. What did you guys think of this creepy duo?