Tobi

, who posed as when first introduced, is a founder of Konohagakure and Akatsuki, and the former leader of the Uchiha clan. When he joined Akatsuki as Tobi (replacing Sasori), he was partnered with Deidara, revealing himself as Madara after Deidara's death. He was once the Mizukage of Kirigakure, although it is unknown when.

Background
Decades before the start of the series, Madara grew up in constant competition with his younger brother, Izuna Uchiha, who were both known as the most gifted members of their clan. Their competition led to both gaining the Mangekyo Sharingan, and, with it, they were able to take control of the Uchiha clan, Madara acting as its leader. Even by his clan's standards, Madara's chakra was unusually strong. Under his leadership, the clan conquered all they came across, but, over time, he began to lose his sight because of the Mangekyo Sharingan. To regain his vision, he took his brother's eyes (an act Madara said his brother had consented to), allowing him to continue to lead the Uchiha to prosperity.

In the years that followed, the Uchiha constantly clashed with the equally powerful Senju clan. To bring an end to the constant fighting, the leader of the Senju, Hashirama Senju, approached Madara with an offering of peace. Although Madara never wanted peace with the Senju, the rest of the Uchiha wanted to end the fighting, and Madara had no choice but to go along with their decision. The Senju, the Uchiha, and all the clans they had conquered came together to form the village of Konohagakure. Against Madara's wishes, the villagers selected Hashirama as the village's First Hokage. Madara feared that Hashirama would oppress the Uchiha, and tried to rally support for challenging his leadership. Rather than help him, however, the Uchiha turned their backs on him, believing his only motive was greed.

Abandoned by his clan, Madara left the village so that he could return to challenge Hashirama in battle. They fought at the site that would someday be called the Valley of the End, where, although Madara called upon the Nine-Tailed Demon Fox, he was defeated, and was believed to have died. Madara faded into memory, and, in time, would found Akatsuki and become Kirigakure's Mizukage.

Twelve years before the start of the series, the Nine-Tails attacked Konoha. Although Madara denied having had any involvement in the attack, Itachi Uchiha and Minato Namikaze said that the Nine-Tails was under Madara's control at the time. A few years later, he infiltrated Konoha to try and rekindle the flames of war. He was found by Itachi first, who convinced Madara to spare the village in exchange for helping to wipe out the Uchiha clan for deserting him decades earlier. Madara complied, training Itachi and providing assistance. Itachi never truly trusted Madara, however, and kept an eye on him for the rest of his life.

Tobi
To keep in Akatsuki's shadow, Madara eventually took on the disguise of Tobi, giving orders to Pain in secret. He wears an orange, swirl-patterned mask that reveals only his right eye. When he trained Itachi, he wore a slightly different mask with black swirl-like patterns on it, and his hair was cut a little shorter. His hair is cut down completely from the days of Konoha's founding, and he wears a uniform consisting of a number of bolts and pins, which is usually concealed by his Akatsuki cloak.

While acting as Tobi, he is carefree and goofy, something that annoys most of the other members. Deidara, who believed all within Akatsuki should be serious and calm, was not pleased with Tobi's childish personality, and frequently attacked the latter in a comedic fashion when annoyed. Apparently, Madara is very committed to keeping his identity secret, as he has been seen keeping up his goofy appearance even when no-one was around (at least during the anime's filler arc). Kisame and Zetsu, on the other hand, somewhat appreciate Tobi's ability to brighten up a gloomy organization such as theirs.

Personality
Madara exhibits a very calm and serious personality. He speaks with less formal diction, such as not using honorifics, and shows typically "villainous" arrogance. He spoke down to Pain (going so far as to refer to him as a "minion") and has great faith in his own abilities, only acting polite to Sasuke Uchiha. He will abandon his normal personality in favor of the Tobi personality when the situation calls for it, as he did when distracting a group of Konoha ninja.

Madara has shown great ability in manipulating others to do his work for him. Minato believed that he was using Pain's ideology against him in order to control him. He similarly befriended Sasuke in order to get him to join Akatsuki by telling him about Itachi's past, even though he has an apparent interest in Sasuke and his abilities. While Akatsuki's goal to gain the tailed beasts is believed by most of the members to be a step in gaining control over the world, Madara implied that the real reason is to restore his Sharingan's power.

Rescue Gaara arc
After the death of Sasori, Madara, as Tobi, appeared with Zetsu collecting Sasori's ring. He expressed interest in joining Akatsuki, believing that finding the ring would grant him membership. They then found Deidara's arm and the ring it wore, believing Deidara to be dead too. When Deidara appeared and demanded that Tobi give him his arm back, Tobi refused, prompting Deidara to try and choke him to death.

Three-Tails Arrival arc
Tobi was accepted into Akatsuki as Sasori's replacement and Deidara's new partner. He was assigned to capture the Three-Tailed Giant Turtle, and Deidara accompanied him. In the anime, during their search, they stopped to get a bite to eat at a dango shop, and Deidara waited anxiously for Tobi to remove his mask so that he could see what he looked like underneath, but he turned away, hiding his face. When he finished his dango, they split up and went in different directions. Tobi eventually found the lake and saw Sakura, Shizune, Hinata, and Ino on the lake using the Four-Corner Sealing Barrier. He then figured out that the technique was to seal the Three-Tails, and went after Deidara to inform him of his discovery.

After Tobi watched Deidara kill two ANBU, he congratulated him. They both discovered the Three-Tails inside the lake. Deidara used his clay to make it appear outside, after which Tobi tried to convince Deidara to fight it in his place. The beast began chasing him, and Deidara used one of his bombs on it while it was distracted. The rest of the battle went unseen. Afterwards, Tobi started talking about how his jutsu was flawless, and now he understood why he had been assigned to the mission. Deidara retored that he wouldn't have got far without his clay. Tobi later fell asleep atop the Three-Tails after making another cheeky comment, much to the anger of Deidara, who "woke him up" by detonating a clay bomb next to him.

Hunt for Uchiha arc
Before sealing the Four-Tailed Monkey, Akatsuki learned Sasuke Uchiha had defeated Orochimaru. Once the sealing was complete, Deidara, angry that he had not got to kill Orochimaru, brought Tobi with him to kill Sasuke instead. They found and confronted Sasuke, and Tobi was given the job of providing assistance for Deidara during the battle. After some initial taunting from the duo, Sasuke surprised them both with his extreme speed and ran his sword straight through Tobi, apparently disembowelling him. Tobi then suddenly stood up again, complaining about the speed of the attack. The battle ultimately didn't go in Deidara's favor, so he used C0 in an effort to kill Sasuke at the loss of his own life. Zetsu reported to the remaining members of Akatsuki that Tobi had been killed too, prompting Pain to remark that he was easily replaceable.

It was soon revealed, however, that Tobi had survived, as he met with Pain and Konan in Amegakure. Tobi was now shown in a completely different light, and was revealed to actually be Madara, the real leader of Akatsuki. His entire demeanor and personality had changed during the appearance. He commented that Sasuke was developing nicely, and then instructed Pain to capture Naruto Uzumaki, the host of the Nine-Tails. He later appeared to distract the 8-Man Squad while Sasuke fought with Itachi. The Konoha ninja had no success in striking him with their attacks, so Shino Aburame volunteered to fight Madara one-on-one. With his bugs, Shino was able to box-in and catch Madara, but Madara was able to escape from this as well. Zetsu then arrived to inform him that Sasuke had killed Itachi. Madara pointed out that he had known that this would be the outcome, and went to see Sasuke. Before leaving, his Sharingan was spotted by Kakashi.

Madara tended to Sasuke's wounds and, when he woke up, offered to tell him about Itachi. Madara tried to befriend Sasuke by removing his mask and revealing his Sharingan eye, something that caused Itachi's Mangekyo Sharingan to form in Sasuke's left eye and which made him use Amaterasu on Madara, who quickly retreated into the darkness of the cave. After stopping the black flames, Madara then appeared again with his mask back on, and began to muse about how Itachi never ceased to amaze him. After Sasuke asked what he was talking about, Madara revealed that Itachi had most likely set it up so that the sight of his Sharingan would trigger the Amaterasu he had sealed within Sasuke. After Sasuke complained that he was making no sense, Madara revealed that it was to protect him, and, when Sasuke still didn't believe him, Madara said how it all must sound crazy but assured him that he was telling the truth, and introduced himself as the man who had helped Itachi on that fateful night. He told Sasuke about the Uchiha clan's history, Itachi's secret life, and the lengths he had gone to keep Sasuke and Konoha out of harm's way. Sasuke, regretting that he had killed Itachi now that he knew the truth, resolved to destroy Konoha for forcing Itachi into the life he had lived.

Hunt for the Eight-Tails arc
Madara convinced Sasuke and the other members of Taka to start working with Akatsuki, the two groups having Konoha's destruction as a mutual goal. Before they could do that, however, he stated that Akatsuki needed the two remaining tailed beasts. Since Pain was still working on capturing Naruto, Madara sent Taka to capture the Eight-Tailed Giant Ox. After Taka left, Madara spoke with Zetsu, discussing Akatsuki's actions up to that point. He went on to say that, although they had lost five talented ninja, all of their efforts had brought him closer to "making Sasuke his".

After Taka captured the Eight-Tails' host, Sasuke gave it to Madara for Akatsuki to seal. During the extraction process, it was revealed to be a fake. Madara was shown to remain silent, as Kisame commented that Sasuke had been fooled in the latter's attempt to capture the jinchūriki.

Invasion of Pain arc
After Nagato's death, Zetsu, after seeing (and "recording") everything that had transpired in Konoha, went back to the Akatsuki hideout to explain the situation to Madara. He pointed out that Konan was not coming back to Akatsuki, with Nagato being dead. Analyzing everything, Madara then sent Kisame to retrieve and capture the Eight-Tails, in which Taka had failed, as he said that he himself had "another matter to attend to".

The Summit of the Five Kage arc
Anticipating Sasuke's betrayal, Madara intercepted Sasuke and his team on their way to Konoha. Madara revealed that Konoha had already been destroyed, and that Naruto had single-handedly defeated Pain. Madara also explained that Danzo had been made the acting Sixth Hokage, and was scheduled to meet with the other Kages on the matter of Akatsuki. After Sasuke left with Taka to kill Danzo at the summit, Madara explained to Zetsu that Nagato had betrayed him, as he had used Outer Path: Samsara of Heavenly Life Technique, and stated that it was supposed to be for him. Madara also explained that he had planned to sync Sasuke with the Demonic Statue of the Outer Path, and that Naruto had "thrown a wrench" into his plans. Madara then decided that it was time to come out of the shadows and to commence with the.

Abilities
Most of Madara's abilities are still unknown. He is thought to be the strongest Uchiha to ever live, and one of the most gifted ninja in history. He was described as a "very powerful ninja" by Minato Namikaze himself. He has also been noted to have been born with particularly powerful chakra, which he states is the reason for his "stubborn refusal to die". Even the Nine-Tails mentioned that Madara's chakra is even more sinister than its own. One of the abilities he has actually displayed is his speed, which, as Tobi, was apparently his only claim to fame. To that end, Kisame commented "he is a good runner". Madara also appears to have immense strength, as he was able to stop a slash from Suigetsu's giant sword with a single arm.

He was armed with a giant kusarigama war fan attached to it during the time of Konoha's founding, fitting with his clan's name, which means "paper fan". He is also said to have been able to summon the Nine-Tails. It is unclear if this referred to the use of the Summoning Technique or if he could produce enough human malice to bring it to his location.

Mangekyo Sharingan
During Itachi's fight with Sasuke, it was revealed that Madara Uchiha and his younger brother, Izuna, 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 Izuna's Mangekyo Sharingan which led to him acquiring immortality. With it, Madara never had to fear the risk of losing his eyesight again. Madara's knowledge and mastery of this powerful Dojutsu allowed him to fight on par with Hashirama, and also gave him the power to forcibly subdue the Nine-Tails.

Teleportation
Madara shows the ability to recover from debilitating or even fatal blows. After being slashed across the midsection by Sasuke's sword, he collapsed, only to stand up again a few seconds later and complain about the speed of the attack. The same things occured when Naruto hit him in the back with a Rasengan, where the attack literally phased through him, avoiding damage. His ability's consistency is confirmed when Sasuke attempted a Chidori on him, and, as predicted, he phased through Madara as Naruto had done earlier.

Madara also shows the ability to travel long distances within relatively short timespans, escaping the final explosion created by Deidara and reappearing in Amegakure within a very short period. It was speculated by Kakashi that he uses time/space Ninjutsu to instantly send himself or even parts of his body to different locations or some sort of void and then instantly bring them back. It is revealed that Madara can find the exact location of a person and warp himself to that place, stating that it is in his power.

Past Speculation
Before Tobi was revealed to be Madara Uchiha, several fans hypothesized that he was Obito Uchiha, as his only shown eye was the opposite of the eye that was inserted into Kakashi. They also have similar personalities, as well as the same hairstyles. The spelling of Obito was also similar to Tobi, creating the fan reference of ObiTobi, or Tobito. Even though Tobi has been referred to as Madara several times in the series, some fans still insist that Obito is somehow connected to Tobi or Madara.

Trivia

 * The phrase "Tobi is a good boy" has proven to be very popular among the Naruto community. Although not said by Tobi himself (Zetsu's white half actually uttered the phrase to his black half after stating Tobi's intentions of joining Akatsuki wasn't so simple to accomplish), many have found the comment to be rather hilarious and, as such, Tobi is depicted as a carefree child or a good-natured character in many fanmade art and videos on YouTube while incorporating the phrase. Many have altered the phrase, after Tobi revealing that he is Madara, saying "Tobi is a bad boy".
 * Although Itachi claimed that Madara had created Akatsuki in chapter 386, Pain said that he created it in chapter 436.
 * can be translated as "spots". Tobi can be translated as, or as . The latter translation connects Tobi with Taka through the Japanese proverb , meaning that an extraordinarily gifted child can be born from ordinary parents.
 * According to the third Naruto databook (despite Tobi and Madara being the same person, the databook gives them separate entries):
 * Madara's hobby is falconry (as Tobi, accompanying Deidara).
 * Madara's favorite food is inarizushi, while his least favorite is roe.
 * Madara's favorite word is "secret".
 * Tobi/Madara will be playable in the upcoming game, Naruto Shippūden‎: Narutimate Accel 3.