Kakuzu

Kakuzu was a tall, muscular man, second in height in Akatsuki (after Kisame Hoshigaki). He wore a white hood and a black mask on his face with his eyes being the only visible part. Underneath, his mouth was stitched together at the edges, and his hair was long and untidy. His eyes have an unusual coloring: green pupils and red scleras. His clothing included the traditional Akatsuki cloak and the forehead protector of his home village with a scratch in the middle which symbolized that he was no longer loyal to it. He also had dark green nail polish and his Akatsuki ring with the kanji forNorth (北, hoku) was placed on his left middle finger. His entire body was covered with stitches and appeared to be sewed together. This was a result of the unique jutsu that he possessed - Earth Grudge Fear. On his back were four masks each resembling those of ANBU where he stored his additional hearts.

Kakuzu first appeared with his partner, Hidan, in their pursuit of the Two-Tailed Monster Cat's jinchūriki, Yugito Nii, who revealed she allowed herself to be cornered, in order to spring a trap on them and eliminate them herself. Yugito then transformed into her full demon form, a large flaming cat, but the Akatsuki duo still managed to defeat her, and gave her body to Zetsu, before they continued to the Land of Fire.
On their way, Kakuzu decided to attack the Fire Temple, in order to collect the bounty on the head monk, Chiriku, who was listed in the bingo book with a thirty million ryō bounty. They slaughtered most of the other monks during the event, but one escaped to warn Konoha of the incoming threat.
Upon receiving the notice, Tsunade assigned the Nijū Shōtai to track down and eliminate Kakuzu and Hidan. Meanwhile, Kakuzu took Chiriku's body to a bounty station hidden in a bathroom, while Hidan chose to wait outside. When Kakuzu finally left the bathroom after counting the money, he found a Nijū Shōtai team, led by Asuma Sarutobi, attacking Hidan. He attacked Shikamaru Nara in order to free Hidan, but was forbidden from further participation in the battle by the overconfident Hidan himself. Kakuzu complied, but insisted that he would get to have the thirty-five million ryō head of Asuma afterwards. In the ensuing battle, Hidan managed to ingest Asuma's blood to start his curse jutsu ceremony on him, but Shikamaru was able to stop him with his Shadow Possession Technique. When Asuma managed to decapitate Hidan, Kakuzu finally intervened, and reattached Hidan's head back to his neck using the threads in his body. Kakuzu then fought with Kotetsu and Izumo, easily holding the two off, while Hidan dealt a fatal blow to Asuma. Their battle was interrupted by the appearance of another Nijū Shōtai team, but they easily fought them off, until they were summoned by the Akatsuki leader to seal the Two-Tails. Hidan and Kakuzu retreated to a secluded area, where they spent three days sealing the Two-Tails (and in the manga, another three days sealing the Three-Tailed Giant Turtle).
After the sealing was complete, Kakuzu and Hidan set out on their search for the Nine-Tailed Demon Fox's jinchūriki (Naruto Uzumaki), only to be cut off by Team 10 (with Kakashi Hatake as the leader in place of Asuma). Shikamaru used Asuma's chakra knives to capture both the Akatsuki members in place with a trick, but Kakuzu had discovered the trick beforehand, and, using a separated arm, broke free. Because of his ability to harden his skin, Kakuzu proved to be largely invulnerable to subsequent attacks. Kakashi, however, was able to analyse Kakuzu's hand seals, and pierced Kakuzu's heart with his Lightning Cutter, exploiting the weakness Kakuzu's earth-based jutsu had against lightning-based ones.
While this would normally be fatal, Kakuzu had five hearts (now four) in his possession, and thus recovered fairly quickly, sending a counterattack to Kakashi. Removing his cloak, he revealed four masks on his back, one of which was now broken by Kakashi. Each mask contained a heart, the broken one having given its heart up to keep Kakuzu alive. The four masks broke free from his back into separate entities, with the broken one dissolving after doing so. Each mask was able to attack with a specific and powerful elemental attack, making Kakuzu almost too much for Team 10 to handle. While Kakuzu set his sights on replacing his lost heart with Kakashi's, Shikamaru dragged Hidan away from the battlefield into some woods, with his Shadow Possession Technique, for a one-on-one fight.
Ignoring the other two for the most part, Kakuzu focused on taking Kakashi's heart. Though Kakashi was unable to handle Kakuzu and his mask creatures, he was saved when Shikamaru tricked Hidan into using some of Kakuzu's blood in his curse ritual, which Kakashi had collected in a capsule earlier when he pierced Kakuzu's chest, and had handed it over to Shikamaru. This resulted in Hidan unintentionally destroying Kakuzu's main body's heart. Seeing this, the Lightning mask allowed its heart to be absorbed by Kakuzu's body, bringing him back to life. In addition to that, Kakuzu also had the two other Fire and Wind masks to combine with him, making him even more powerful. He then caught the rest of Team 10 with his threads, hoping to replenish his stock.
Team 10 was saved by the arrival of Team 7, among them being Naruto, who decided to fight Kakuzu himself, who at first did not view Naruto as a threat. This changed when Naruto unveiled his newly developed technique, Wind Release: Rasenshuriken, which Kakuzu recognized to be dangerous if it ever connected with him. Naruto's inability to maintain the technique for more than a few seconds put Kakuzu at ease, especially since its failure almost allowed him to kill Naruto (although Yamato and Kakashi saved him), but decided to fight in his long-range mode just to be safe. As Naruto tried the Rasenshuriken once again with his shadow clones, Kakuzu attempted to crush Naruto with his threads from a distance, but was surprised to discover that it was a shadow clone that he had destroyed, and, subsequently, the real Naruto shot up behind him, using the technique effectively this time.
Left with no usable hearts after being battered by Naruto's technique, Kakuzu lamented being defeated by those he considered "kids". Kakashi assured Kakuzu that the previous generation being surpassed by the next was perfectly natural, and one of the "never-ending cycles of life". Kakashi then finished him off with a Lightning Cutter.
Kakuzu's corpse was later taken back to Konoha to be autopsied by Tsunade in regards of the Rasenshuriken's capabilities, and it revealed that Kakuzu was damaged at a cellular level by it.

Kakuzu was a greedy, miserly individual, arranging goals in terms of the highest profit he could gain from them, and was often unwilling to involve himself in something unless there was something to gain. He even remarked that money is the only dependable thing in the world. Due to this end, he referred to himself as the "Treasurer of Akatsuki". Given his friendly relationship with Ginji, his bounty officer, it would seem he collected bounties rather frequently to earn cash, and did so (or at least tried) during his missions on several occasions. The frequent side-tasks and devotion to money were both major points of contention between Hidan and Kakuzu. He also seemed to respect an opponent who thinks, as shown with his reaction to Kakashi's counters to Kakuzu's masks, and Shikamaru's quick analysis of Hidan's curse, even mentioning Shikamaru would have been a good bounty in the future.
Out of all the Akatsuki members, Hidan and Kakuzu displayed the most animosity towards each other, since neither of them were very fond of each other's interests. The two often traded barbs with one another, Kakuzu's usually having better timing than Hidan's. Hidan had shown great annoyance with Kakuzu's greed and occasional habit of doing or saying blasphemous things, such as attacking a temple and killing the head monk for the bounty on the monk's head. Kakuzu, in turn, disliked Hidan's religion, believing the rituals associated with it to be a waste of time. Kakuzu was also rather impatient with Hidan's drawn-out speeches and battle style.
The only reason that Kakuzu put up with Hidan was because he couldn't get rid of him. Due to his violent temper, Kakuzu often killed anyone close by when enraged. Hidan, therefore, was the perfect partner for Kakuzu, because of Hidan's inability to die. Kakuzu's somewhat indiscriminate attack style also made Hidan an ideal partner, since Kakuzu didn't need to worry about catching his partner in the crossfire.
Despite his obsessive personality and violent rages, Kakuzu was much more cautious than his partner, and was not as arrogant, never mindlessly rushing into battle like Hidan. Kakuzu frequently warned Hidan not to let his guard down, and then teased Hidan when he inevitably did. Kakuzu apparently seemed quite willing to follow orders. When ordered to retreat by the Akatsuki leader, Kakuzu complied immediately (while Hidan attempted to argue), despite the rather large bounty he could have received by taking Asuma. He seemed to forget the greater goals of the organization when enraged, as he attempted to kill Naruto, in spite of Akatsuki's need to capture all the Tailed Beasts alive.