Tobi

also known as in Akatsuki, was first introduced as Zetsu's subordinate. Tobi "became" a full Akatsuki member after Sasori's death and afterwards wore the same ring as Sasori having recovered it after his death and taking his place as Deidara's partner. After Deidara's death, he revealed his real name and that he had been the one giving Pein orders, making him the true leader of Akatsuki. Only Konan and Pein who were the only Akatsuki members known to have been present at that meeting, Zetsu, and Itachi Uchiha and recently Kisame (who recognized him as the Mizukage) knew his true identity. He is one of five known characters who can use the Mangekyo Sharingan, the other four being his younger brother, Itachi Uchiha, Sasuke Uchiha, and Kakashi Hatake.

Background
Eighty years ago, when shinobi were battling as individual clans, not as villages - among a countless number of them, two clans emerged as the strongest: the Uchiha clan and the Senju clan of the forest. Madara was born with a particularly strong amount of chakra, which he states due to his "stubborn refusal to die". His chakra was strong even for the Uchiha clan, who were known for having strong chakra. He was also the first to activate the Mangekyo Sharingan. He had a younger brother, who was equal to him in every way and who also awakened the Mangekyo Sharingan. Together they ruled over the Uchiha clan, with Madara taking the role as leader. But eventually Madara went blind, unaware of any side effects of the Mangekyo Sharingan at the time. He became increasingly desperate to regain his eyesight. He killed his brother and stole his eyes (although he claims that his brother willingly gave his eyes up to Madara for the sake of the Uchiha clan), so that he would have the strength to continue leading Uchiha. At some point in Madara's early life, by the decision of the entire Uchiha Clan except for him, he formed an alliance with the Senju Clan of the Forest, Hashirama Senju's clan, and together with its leader, the future First Hokage, Madara founded Konohagakure.

However, after Hashirama was chosen to be the First Hokage of Konoha, Madara feared that the Uchiha clan would lose supremacy and he sought the help of the Uchiha in his challenge for leadership. The Uchiha clan, however, refused, believing he was greedy, and called him a monster who stole his own brother's eyes just for his own desires. None of the Uchiha would help Madara, and he decided to leave the village. Feeling hurt, he came back and wanted revenge against Konohagakure which led to a legendary battle at the Valley of the End against Hashirama. During the battle, Madara used his Mangekyo Sharingan to take control of the Nine-Tailed Demon Fox and used it in a desperate attempt to kill the First Hokage. Madara, however, was ultimately defeated and was presumed by most to have died after the battle. Madara fled, and was never seen or heard of again out in the public for decades. To commemorate the battle, two statues, one of Madara and the other of the First Hokage, were carved into the earth around the waterfall. It is for this reason that Naruto Uzumaki and Sasuke Uchiha's fight at that location was noted to be ironic.

Madara created the criminal organization known as the Akatsuki to look over problems. He hid behind the shadows and placed Pein as the figure-head leader, with Madara giving Pein orders from the background. Outside of Pein, the only members who are shown knowing Madara's position as the true leader are Konan, Kisame, Zetsu and Itachi.

Itachi Uchiha believes it was Madara himself that controlled the Demon Fox to attack Konoha, though Madara denies this, saying that the fox was a natural disaster. Nevertheless, when he came to destroy the entire village of Konohagakure in revenge, he met up with Itachi, who had already been assigned his mission to kill his clan. Itachi successfully talked Madara into only killing the Uchiha Clan as long as he left the rest of the village alone. Madara also taught Itachi about the Mangekyo Sharingan, helping him by teaching him how to unlock its true power. After Itachi killed off the Uchiha clan because of orders from the Leaf Village, Madara let Itachi into Akatsuki for unknown reasons. Itachi refers to Madara today as "a pathetic shell of his former self, no longer worthy of being called the greatest Uchiha."

It has also been recently revealed that at some point after being presumably killed, Madara took the role of Mizukage.

Tobi
To keep in Akatsuki's shadow, Madara eventually took on the guise of Tobi and was placed within Akatsuki as Zetsu's subordinate. As Tobi, Madara wears an orange mask, with swirls focused around the right eye, that covers his entire face outside of his right eye. Before wearing the swirl mask, Madara wore a similar mask, with markings across it, covering his entire face but the right eye.

Furthermore, Tobi has several bolts or pins present on the arms of his uniform, obscured by his Akatsuki cloak. While acting as Tobi, unlike others within Akatsuki, Tobi is carefree and goofy, but Madara uses a very formal and correct manner of speech.

While Tobi greatly respects his other members, referring to Deidara as Deidara-senpai in the Japanese version, most of the other members tend to get easily annoyed by Tobi. Deidara, who believes all within Akatsuki should be serious and calm, is not pleased with Tobi's childish personality, and frequently attacks Tobi in a comedic fashion when annoyed. Kisame, on the other hand, somewhat appreciates Tobi's ability to brighten up a gloomy organization such as theirs.

As Tobi, Madara has not been seen wearing a forehead protector, probably to seal his identity, though he already has a mask covering his forehead, so this could also be why it is not visible.

Abilities
Most of Madara's abilities are still unknown. He is known to have an advanced Mangekyo Sharingan, and to make use of space-time ninjutsu speculated by Kakashi to be even greater than the Fourth Hokage's space-time ninjutsu. Since the Uchiha clan is known for its fire techniques, it is also speculated that he knows advanced fire techniques as well. He was armed with a giant fan during the time of Konoha's founding, which may explain the origin of a paper fan being the symbol of the Uchiha clan. He and Deidara were able to defeat the Three Tails, but Madara (as Tobi) was never shown doing anything but running away from it. After the battle, which goes largely unwitnessed, he claims to have knocked it out with a single attack. Deidara disagrees with the assessment, claiming that it was his "artistic contribution" (exploding clay) that allowed them to win. While as Tobi, Madara is also shown planting Deidara's clay minefields underground during a later battle. Itachi refers to Madara as being an "invincible immortal", which is further evidenced by continued existence despite his advanced age and his surviving the battle at the Valley of the End despite witnesses belief that he died.

Madara shows the ability to recover from what are presumably debilitating or fatal blows. After being slashed across the midsection by Sasuke's sword, he collapses, only to stand up again a few seconds later and complain about the speed of the attack, and later when Naruto hits him in the back with a Rasengan. The attacks literally phase through him, avoiding damage. He is also seen being hit by Sasuke's Amaterasu but emerging unharmed.

Madara also shows the ability to travel long distances within relatively short timespans, escaping the final explosion created by Deidara and reappearing in Amegakure, then travelling to the Valley of the End all within a very short time span. It is speculated by Kakashi and Sakura that he uses space/time ninjutsu to instantly send himself or even parts of his body to different locations or some sort of void and instantly bring them back. This was noted in his fight with Naruto, Sakura, Sai, Kakashi, Yamato, Kiba, Hinata, and Shino when Naruto attacked with a full powered Rasengan that phased right through him, and also when he escaped Shino's bugs even though they were completely surrounding his body. Second, when Madara criticized Zetsu's slow speed, Zetsu responds with a remark implying that his jutsu enables him to move at very high speeds.

After he escaped Deidara's final explosion, it is revealed that he possesses the Sharingan, shown visible through the opening of his mask. The demon fox mentioned that Madara's chakra was sinister, more sinister than its own. Madara was the only person capable of taming the demon fox which was said to only come where human malice collects and festers, yet he was able to use the Sharingan to tame the tailed beast.

During Itachi's fight with Sasuke, it is revealed that Madara Uchiha and his younger brother were the first members of the Uchiha to activate the Mangekyo Sharingan, and used its power to take over the clan. After implanting his brother's eyes into his own body, Madara then awakened a new "eternal" Mangekyo Sharingan, a combination of his own and his brother's Mangekyo Sharingan which gave him untold amounts of power without the risk of losing his eyesight. It was with this power Madara was able to forcibly subdue the demon fox. He is said to be the strongest Uchiha.

Rescue Gaara arc
Madara is first introduced as Tobi alongside Zetsu collecting the rings of Deidara and Sasori. While Sasori's ring is collected, Deidara, who managed to live, appears and reclaims his own ring. After annoying Deidara three times, Deidara responds by comically choking Tobi with his feet. Using Sasori's ring, Tobi manages to join Akatsuki, though Zetsu claims it isn't as easy as collecting the ring.

Hidan & Kakuzu arc
Tobi, who by now has successfully joined Akatsuki, is partnered with Deidara and sent to collect the Three-Tailed Beast. After Deidara reveals that this is Tobi's mission, Tobi, panicking, is seen only running away from the Three-Tails in a comic fashion. After the battle, which goes mostly unwitnessed, Tobi triumphantly claims to have defeated Three-Tails in a single blow, though Deidara disagrees. Tobi later falls asleep atop the Three-Tails after making another cheeky comment, much to the anger of Deidara, who "wakes him up" by detonating a clay bomb next to him.

Hunt for Uchiha arc
Tobi is seen following Deidara, who is chasing Sasuke Uchiha, and eventually join Deidara's battle with Sasuke, though he does little besides laying mines for him and serving as a distraction. When Deidara prepares to use C4, Deidara orders Tobi to flee, though, while escaping C4, Tobi is later shown getting killed by Deidara's final explosion.

It is later revealed, however, that Madara lived, as he is seen ordering Pein in Amegakure just a few minutes after Deidara's death. Madara gives Pein the order to personally capture Naruto Uzumaki. Madara then travels to the Valley of the End on his own statue as Tobi, and while resting there comments that Sasuke Uchiha's Sharingan is growing more powerful.

Madara appears as Tobi to stop Naruto, Hinata, Yamato, Kakashi, Sakura, Shino, Sai, and Kiba from searching for Sasuke and Itachi Uchiha, and phases through all attacks the group sends, even a full-powered Rasengan from Naruto Uzumaki and a full ranged attack from Shino even after completely covered in bugs. Tobi continued to fight the 8-Man Squad until Zetsu arrived to tell him that Itachi had died, which was no surprise to Madara. Before he took his leave, the Sharingan, which he possessed, was spotted by Kakashi. Tobi and Zetsu arrived at Itachi's battlefield, to recover the bodies of the two brothers, before the 8-Man Squad caught up to them. Off in a cave somewhere, Sasuke is startled to see Tobi, who says he gave him some first-aid, which also deteriorates the curse seal. Madara then claims to know the truth about Itachi as he removes his mask revealing a glimpse of his Sharingan. In the next chapter, Sasuke is shown using Mangekyo Sharingan but it only appears in his left eye, using Amaterasu. Tobi explains that Itachi gave all of his eye techniques to Sasuke, as a backup plan in case Sasuke ever met him.

He then continues by saying that Sasuke had to question him, calling it his mission and duty. Furthermore he begin revealing that Itachi, risked all to protect the Shinobi World, The Leaf Village and most of all his little brother. He tells Sasuke about how the Senju clan and the Uchiha clan were rivals. When the Senju clan wanted to form an alliance with the Uchiha clan, Madara was the only one against it. He soon agreed and together they formed the Konoha. For the position of Hokage, everyone in the village and the land of Fire chose Hashirama. Madara saw that the Uchiha clan was losing supremacy, and chose to oppose Hashirama. But no one among the Uchiha followed him. They despised him saying that he was greedy and stole his own brother's eyes to save himself. He left the village and bent on revenge challenged the village. Madara and Hashirama fought. Although Madara controlled the Nine-Tailed Demon Fox during the battle, he was defeated in the place now known as the Valley of the End, probably due to Hashirama's Tailed beast-suppressing jutsu. After the battle, he was presumed dead by most of the village. Madara then tells Sasuke the truth of Itachi.

Sasuke's Revenge
After the formation of Hawk, Madara removes his mask before Kisame Hoshigaki, who recognizes him as the Mizukage. When the planning began, Madara officially allied Akatsuki with them for their goal to destroy Konoha. Madara states that they will use the Tailed beasts to destroy Konoha and will require Hawk to capture the Eight-Tailed beast. Afterwards Madara met with Zetsu to discuss the fate of the old Akatsuki members, and more importantly how Madara now has Sasuke.

Madara later traveled to Pein and Konan's home where he learned of Jiraiya's death. He then questioned Pein's abilities which, only to receive a cold stare and lecture from Konan about her old comrade's power. Madara then tells them about Sasuke going after the Eight-Tailed Beast which he is sure he will accomplish and then leaves.

Past Speculation
Before Tobi is revealed to be Madara Uchiha, several fans hypothesized that he could be Obito Uchiha, as his only shown eye was the opposite of the eye that was inserted in Kakashi, which replace Kakashi's destroyed left eye in the manga-exclusive Kakashi Gaiden, and their similar hair styles. Also, they both act in the same goofy way, and Tobi has claimed to be a good boy, while Obito was a good boy. Furthermore, Tobi is seen to have pins in his body under the coat, and Obito's body was crushed. The spelling of Obito was also similar to Tobi, creating the fan reference of ObiTobi, or Tobito.

Another fan speculation is that Pein, who now is discovered to have multiple bodies, could have used the remains of Obito to reconstruct the body and revive Madara in the body of Obito, which contained Sharingan only within the right eye, the same eye that Madara has been shown using the Sharingan. It is also possible that Pein employed Kakuzu, who was able to reattach Deidara's arms after they were severed, and could have done similarly with Obito and Madara.

One more speculation is that Orochimaru, who was able to use the Summoning: Impure World Resurrection, as demonstrated in the fight with the Third Hokage, and who was once a member of Akatsuki, probably used or learned it there. And so, it is possible that the body of Obito has been reanimated and the spirit of Madara has been implanted into him using another forbidden jutsu.

Fans also speculated that Madara could also be Danzo, Tobi has bolts on the same arm that Danzo has covered up. Similar hair styles. Not only that, he and Madara share the same hate for the First, Second, and Third Hokage's Teachings and Philosophy. Plus Madara hates the Senju clan, and the first and second were both Senju. Danzo also despises Tsunade for being the Grand-daughter of the First. Danzo also has the same eye covered up that Madara has his Sharingan. Kisame's revelation of Madara being Mizukage offers more support to this theory as Danzo's Root is said to use extremely similar methods to Kirigakure earlier on, the education that led to the village being referred to as the Village in the Bloody Mist.