The Uchiha clan (うちは一族, Uchiha Ichizoku; Literally meaning "Uchiha family") was once considered to be one of the most powerful clans in Konohagakure, but is now almost extinct after the events of the Uchiha Clan Massacre.
The Uchiha clan was descended from the elder of the two boys entrusted by the Sage of the Six Paths with the power and will of the way of the ninja. The elder believed that might would bring peace. The Sage chose the younger as more fitting to be his successor, causing the elder to be vengeful. From the younger boy descended the Senju clan who would be the eternal rivals of the Uchiha.
Before the founding of the ninja villages, the Uchiha were one of the many mercenary clans for hire. Because of their Sharingan, the Uchiha clan came to be known as one of the two strongest clans, the second being the Senju clan. Madara Uchiha was particularly powerful, and, upon attaining the Mangekyō Sharingan, he took control of the clan. Under his leadership the Uchiha grew stronger, conquering whatever clans they came upon, such that, whenever the Uchiha clan was hired for a job, the opposing side would hire the Senju.
Hashirama Senju, the leader of the Senju clan, grew tired of the endless fighting, and approached the Uchiha clan with a peace treaty. Madara feared that an alliance would lead the Uchiha to ruin, but his clan disagreed, and he was forced to accept. The two clans came together to form Konoha, with Hashirama being selected as Hokage. Madara believed that this was proof that the Uchiha would be made subservient to the Senju, but his clan saw this only as his attempt to rekindle the flames of war. They turned their backs on him, and he defected. Following Madara's betrayal, the Second Hokage gave the Uchiha control of the Konoha Military Police Force as a sign of trust. According to Madara, this was really just a way of keeping the Uchiha in check and out of Konoha's governing affairs. Over the years, some Uchiha, such as Setsuna, have figured out this motive's true meaning, and tried to rebel against the village as Madara did, but they find that it was too little, too late to make a difference, as the Senju had already completely suppressed the Uchiha
Decades later, after the Nine-Tails' Attack on Konoha, Konoha began to suspect that an Uchiha was behind the attack. The Uchiha were relocated to a corner of the village so that they could be more easily monitored. The Uchiha interpreted this as confirmation of what Madara had warned them of years earlier, and began to plan overthrowing the village. One Uchiha, Itachi, disagreed with the coup d'état, and informed Konoha's leadership of what the Uchiha were up to. The Third Hokage, Hiruzen Sarutobi, tried to negotiate for a more peaceful approach. This failed, and to prevent an uprising that would create another war, Itachi was ordered to wipe out the Uchiha.
Itachi spared only one Uchiha: his younger brother, Sasuke. Sasuke would spend the next few years trying to avenge their family by killing Itachi, something Itachi had planned for from the very beginning. Once accomplishing this goal, Sasuke learned that Madara was also still alive. Madara told Sasuke about the Uchiha's history and why Itachi had wiped out the Uchiha, prompting Sasuke, with Madara's help, to resolve to destroy Konoha.
The Uchiha were infamous for their especially strong and natural aptitude for anything combat-related, highly powerful chakra, and their proficiency in fire jutsu, having created several and using them more skillfully than any other. Their signature jutsu was the Fire Release: Great Fireball Technique. Clan members were not recognized as adults by the rest of the clan until they could successfully use this jutsu. The Uchiha were also highly known for their mastery of ninja tools. They themselves invented many shuriken techniques which required the use of thin metal wires, one example being the Windmill Triple Blades technique.
The Uchiha clan were most feared for their powerful Sharingan, a kekkei genkai which gives them the ability to see the "colors" of chakra, allowing them to analyze and copy their opponent's skills, along with a number of other abilities. Only a select few members of the Uchiha clan manifested the Sharingan. Due to their natural affinity for battle, and their proficiency with genjutsu, many ninjas considered it more tactically favorable to flee rather than face an Uchiha shinobi in one-on-one combat. Among the techniques granted by the Sharingan, the Izanagi is deemed to be forbidden, due to it renders the user blind in exchange of controlling reality for a certain amount of time. Though the clan was feared for their Sharingan, the eyes have also been transplanted into various characters outside the clan.
Madara discovered that, by the death of one's closest friend, the Sharingan could be taken to its next level: the Mangekyō Sharingan. It gave the user great power, but slowly deteriorated their eyesight. Only by taking the eyes of a sibling could one's vision be restored. Itachi indicated that the intricacies of the Mangekyō Sharingan were only discovered after years of trial and error, implying that many Uchiha throughout history had made the attempt to gain the Mangekyō Sharingan.
The Uchiha clan were one of the founding noble families of Leaf village. The clan itself is said to be descended from the Hyuuga clan who possess the bloodline of the Byakugan eye. Because their clan possessed the Sharingan or "Wheel Eye," the Uchiha excelled at being able to read and fend off attackers. This made them prime candidates to help found the Konoha Military Police Corps. The organization itself would go on to incorporate the Uchiha fan symbol into their official logo.
Select few members of the Uchiha clan possess the ability to activate the bloodline Sharingan eye. This doujutsu (eye skill) gives one the ability to read Genjutsu, Taijutsu and Ninjutsu and then defeat it. As such, the clan member can view a technique being performed and see the tricks and movements required to be able to complete it. However the clan member can not copy techniques which are unique to another bloodline. It also gives one the ability to cast jutsu techniques only possible by possessing the eye.
The clan itself is known for their ties to fire. For a clan ninja to be seen as an adult, they must be able to utilize a Katon (Fire Element) jutsu such as Goukakyuu no Jutsu. Thus is the tie between the manipulation of fire and the mind of an Uchiha member.
