Uchiha Madara

Uchiha Madara was a highly skilled ninja who lived years previously. He helped lead the Uchiha clan and was one of the founders of Konoha. Madara's fame and powerful Sharingan eye chakra was even known to the Kyuubi. Kyuubi regarded this chakra from the cursed bloodline as even more ominous than his own. He would bear witness to this chakra again in the form of Uchiha Sasuke. Madara himself was said to have the ability to control the Bijuu. This ability was apparently similar to the one possessed by Shodai Hokage.
When he was young, Madara and his younger brother competed against each other. Both possessed the Sharingan and attained Mangekyou through their rivalry. With their newfound power, they increased their clan's power and standing. Unfortunately, usage of Mangekyou leads one to blindness and Madara was the first to fall to this side effect. With his eyesight gone, Madara took his brother's eyes in desperation. These new eyes allowed him to see once again and granted him "Eternal" Mangekyou. With these powerful eyes he met representatives of a nearby clan and helped found Konoha. This clan was lead by the man who would become Shodai Hokage. At some point the men had a falling out, and the two did battle at the Valley of the End. It is said the destruction was so great it tore the earth asunder, creating the very valley. Two gigantic statues were later erected on the spot in their honor.
Madara apparently fled, still alive. He would later use his bijuu abilities to secretly direct the Kyuubi to attack Konoha. Kyuubi was stopped and Madara remained underground. The group Akatsuki sought to capture the Bijuu for their own ends. It was revealed that their leader Pain, actually reported to Tobi, one of the new members of the group. There was apparently more to Tobi than meets the eye, as he revealed in an ominous voice that Uchiha's Sasuke's Sharingan was growing powerful. This was something he could recognize with his own Sharingan power, as Uchiha Madara. The exact nature of Tobi and Madara is still unknown.

Hoshigaki Kisame

A highly dangerous S-Ranked criminal, Kisame was an elite Jounin in Hidden Mist Village until he began to assassinate the local Mist feudal lords. Fleeing his village, Kisame then joined the Akatsuki Organization. Kisame was ordered by the leader of Akatsuki to partner with Uchiha Itachi and obtain the Kyuubi demon from within Naruto. The two S-Ranked criminals went to Leaf Village in search of Naruto. Sarutobi Asuma and Yuuhi Kurenai confronted the two, so the ninja began to battle. Kisame used his head-cleaver against Asuma and managed to surprise the Leaf Jounin with its shark skin scales. Kisame drew blood but Asuma was able to recover himself. When Maito Gai appeared, Itachi and Kisame fled.
Later Kisame and Itachi tracked Naruto down to a hotel outside of Leaf Village. They were about to capture Naruto when Sasuke and Jiraiya appeared. Seeing that it was not the right moment, the two Akatsuki members fled. Over the next few years, Kisame and Akatsuki would wait patiently to capture more demon vessels like Naruto.
When Akatsuki members Sasori and Deidara returned from Hidden Sand with the captured Gaara in tow, Itachi and Kisame were directed to delay the pursuing Leaf and Sand ninja. Kisame was eager to get a measure of revenge again Maito Gai who had gave him a hard kick years earlier. Kisame managed to capture Gai's former students in a water prison, allowing himself and Gai to duke it out one on one. Gai was forced to open his gates to avoid Kisame's water attacks. Gai pummeled Kisame and knocked him back to the earth. Gai then learned that the Kisame he fought was not really Kisame himself, but another who was sacrificed to become Kisame in appearance while Kisame himself could fight through him from afar. The delay plan worked, and Kisame and Itachi were able to give Akatsuki enough time to remove Shukaku from Gaara.

Zetsu

Zetsu is the only member of Akatsuki to regularly act without a partner. This is in part a result of his ability to merge with any object and quickly travel to a new location, a feat few other ninja are capable of. Because of this ability Zetsu serves a variety of different positions in Akatsuki, such as a spy that observes and reports on battles of interest or a lookout during Akatsuki's meetings.
Being cannibalistic, he is often sent to dispose of bodies Akatsuki does not want found, mirroring the large venus flytrap that envelops his body. Zetsu's body is split into two half’s, both light and dark, similarly, the two sides have their own personalities and knowledge bases, frequently leading to discussions and arguments between the two. The black half speaks in Katakana in the Japanese manga, while the white speaks Kanji and Kana. He use “Kai” (Boar) ring on his right little.
When Naruto fought Sasuke at the Valley of the End, Zetsu spied on the proceedings. When Kakashi came to retrieve Naruto, he emerged from the ground and watched them return to Konoha. Several years later he watched over Gai and his team who were going to meet up with Kakashi in their search for Akatsuki. Zetsu appears to extend a sixth-type sense from his body to the area around him, rather than by relying on his eyesight alone. Also his different halves seem to have different personalities, with the black side speaking in a strange, unusual manner. He was also commanded at one time to eat the bodies of Sasori's dead subordinates.
Zetsu later appeared in the destroyed former cave base of the group with new recruit Tobi. One of Zetsu's sides favored Tobi and thought of him as a good young man. When Tobi found Sasori's ring, Zetsu debated whether the young man was worthy to replace the former member. He and Tobi then traveled to locate Deidara. Tobi managed to find Deidara's arm. Deidara himself soon arrived to take back his lost limb. Later when Hidan and Kakuzu captured the Nibi Jinchuuriki Nii Yugito, Zetsu arrived to take on the duty of returning her body to their base of operations.

Akasuna no Sasori

Sasori (meaning scorpion) is a former ninja of Sunagakure. He was a legendary puppet master from Hidden Sand who left his village approximately 20 years before the start of the series. His parents died cause of the white fang (Kakashi's father) when he was young, leaving him in the care of his grandmother, Chiyo.
Lacking the love of parents, Sasori left Sunagakure when he got older and joined Akatsuki where he is initially partnered with Orochimaru. After Orochimaru's defection Sasori teamed with Deidara, who looks to him and his artistic knowledge with reverence. Sasori converted portions of his body into puppet parts, retaining a flesh and blood portion of his original self in a chest container. He used the "hitokugutsu" method to turn people into puppets while still alive, allowing him to use their jutsu even after their "death."
In time he even converted his own body into a puppet that has his heart in a container on the left side of his chest, which gives him eternal life and allows him to control hundreds of puppets at once. Each weapon in his puppets' extended arsenal is laced with a poison of Sasori's design that causes extreme pain to the inflicted until they die. He fell in battle to Chiyo and Sakura, hesitating to not avoid the lethal strike of his parents who had been made into puppets. He use “Tama” (Sphere) ring on his left thumb.

Pain

Pain acts as the leader of Akatsuki and the partner of Konan, though he and Konan secretly report to Tobi, appearing in the form of six entirely different bodies that share the same mind, referred to as "The Six Paths of Pain". The only common physical characteristics amongst them are their orange hair color, a number of body piercings, and the Rinnegan ("Samsara Eye").
The Rinnegan, a unique eye technique (dojutsu) characterized by a number of concentric circles around the pupil, allows the wielder to utilize any ninja ability. Pain uses it to share visual information amongst all six bodies, giving them the ability to coordinate offense and defense as if they were a single entity. Each body possesses a unique skill; the body with a large ponytail, for example, can summon a wide array of creatures, while the fat body is able to absorb attacks as a form of defense. Following the capture of one of the six bodies by Jiraiya, a new body appears to replace it. Pain's might was enough to overthrow Amegakure's former governmental body, giving Pain control of the village and god-like status amongst its citizens. He use “Rei” (Zero) ring on his right thumb.

The Akatsuki Organization

The Akatsuki (meaning "Dawn" or "Daybreak"), breaking down the word itself gives us "aka" meaning red (a common color in the group) and "tsuki" meaning moon. This Organization is a criminal organization composed of ten high-level S-Ranked criminals’ ninja that have defected from their village of origin. Many of these are missing-nins who fled their villages after causing death and destruction. Akatsuki members are characterized by their long, dark cloaks bearing red clouds with a chin-high collar. Each also possesses a unique ring, which seems to symbolize one's membership in the organization. Members are partnered together in teams of two, each team sticking together as they traverse the world. Despite this partnership, members tend to have a strained relationship with their peers, only cooperating enough to complete their assignments and showing little concern when another member is killed.
Akatsuki was founded by Uchiha Madara after he was expelled from his hometown of Konohagakure. Though initially meant only to mask Madara's movements, Akatsuki eventually began taking part in assassinations and espionage. By the start of the current storyline, Akatsuki's ambitions grow to plans of world domination. To mark this more dynamic goal, Akatsuki increases its activity throughout the series as it attempts to capture the nine powerful tailed beasts. Each member is assigned to capture a specific beast or its current host, at which point Akatsuki convenes to extract the beast and seal it away for their grand plan. As the Akatsuki leader, Pain, explains it, once all nine beasts have been captured Akatsuki will be able to harness their great strength to start world wars at their leisure. With the world governments unable to deal with the beasts' power, Akatsuki will be turned to for salvation, teaching the world the meaninglessness of fighting and giving Akatsuki complete control in the process.
Their ultimate goal is to control the world; this will be accomplished through three steps. Step One is for the group to attain money. Step Two is to create the first mercenary group. Shinobi villages make money for their country, and for the money to be steady it requires war. Because there have not been any large scale wars in approximately the last decade, the ninja villages were being reduced in size. The Five Great Shinobi Villages could handle the downtrend, but the smaller villages could not. Akatsuki will form their own fighting force with no country allegiance. With this force they will undercut all the other villages and fight their battles for cheap. Then using the bijuu they can create new battles and new wars and gain a monopoly over the whole market. In the end they plan to control all the wars and be powerful enough to even collapse the shinobi villages of the large countries, forcing them to rely on Akatsuki as well. With all that in hand, the group can achieve Step Three, to control the world. It should be noted their goal and plans have been explained by Pain, the man acting as leader. While Pain was separated from the group, he expressed his own desire for the Bijuu, to use them to create a powerful Kinjutsu. It has also recently been revealed that Pain reported to Tobi, who was revealed to be Uchiha Madara. What Madara wants with the Bijuu and powerful Sharingan of Uchiha Sasuke is unknown. He may share Pain's deadly Kinjutsu plan or have his own goal mind.