Madara Uchiha (うちは マダラ)
At the beginning posing as Tobi in the Akatsuki, formerly appeared to be Zetsu's subordinate. Madara, as Tobi, became a full Akatsuki member after Sasori’s death. He later wore Sasori's ring having recovered it after his death and took his place as Deidara's partner. After Deidara's death, he revealed his real name and that he had been the one giving Pain orders, making him the true leader of the Akatsuki. Only Pain, Konan, Zetsu, Itachi Uchiha, and Kisame Hoshigaki (who recognized him as the former Mizukage) know his true identity. He is one of five people who can use the Mangekyou Sharingan, the other four being his clanmates Izuna Uchiha (his younger brother), Itachi Uchiha, and Sasuke Uchiha, along with an unrelated Kakashi Hatake.
According to Madara, 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. Madara was also the first to activate the Mangekyou Sharingan.
He had a younger brother named Izuna who was equal to him in every way and also awakened the Mangekyou Sharingan. Together they ruled over the Uchiha clan, with Madara taking the role as leader. But eventually Madara went blind, due to side effects of the Mangekyou Sharingan. His younger brother gave his eyes voluntarily to protect the Uchiha clan. At some point in Madara's early life, he formed an alliance with the Senju clan, Hashirama Senju's clan, and together with its leader, the future First Hokage, Madara founded Konoha.
However, when 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, refused, believing he was greedy. None of the Uchiha would help Madara, and he decided to leave the village. Feeling hurt and betrayed, he came back and wanted revenge against Konoha which led to a legendary battle at the Valley of the End against Hashirama. During the battle, Madara used his Mangekyou Sharingan to take control of the Nine-Tailed Demon Fox and used it in a desperate attempt to kill Hashirama. 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 Hashirama, were carved into the earth around the waterfall. It is for this reason that Naruto and Sasuke'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 Pain as the figure-head leader, with Madara giving Pain orders from the background. Besides Pain, the only members who are shown knowing Madara's position as the true leader are Konan, Itachi, Zetsu, and Kisame.
Itachi, Jiraya and Minato believe, it was Madara himself that controlled the demon fox to attack Konoha, though Madara denies this, saying that the demon fox was a natural disaster. Nevertheless, when he came to destroy the entire village of Konoha in revenge, he met up with Itachi, who had already been assigned his mission to kill his clan. Madara also taught Itachi about the Mangekyou Sharingan, helping him by teaching him how to unlock its true power. After Itachi killed off the Uchiha clan, Madara let Itachi into Akatsuki for unknown reasons.
