Uchiha Clan Histroy

Sharingan - Copying Wheel Eye (Uchiha Clan)
Sharingan is the blood inheritance limit of the Uchiha Clan. The Uchiha are said to be descendants of the Hyuuga, with the Byakugan changing into the Sharingan over time. 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 almost instantly memorize the movements required to be able to complete it, including the needed chakra moldings and seals used. However the clan member cannot copy techniques that are unique to another bloodline and the clan member must have a body capable of meeting the chakra and physical requirements to do the jutsu. This rarely stops the clan member though, as such stressful situations often push their limits farther and allow them to harness their full potential.

The Uchiha clan member is not granted the Sharingan at birth; it is only activated later in life, typically during a time of emotional stress in the heat of battle. The Sharingan itself can be transferred to another non-Uchiha by a medical ninja, such as happened with Leaf ninja Uchiha Obito to his teammate Hatake Kakashi. Because his body was not born to carry the Sharingan, the eye is always activated and it burns Kakashi's chakra when used. To lessen the impact of the Sharingan on Kakashi's body, he normally keeps the eye hidden and out of use. Also of note, is the fact Kakashi, a non-Uchiha, was able to advance the Sharingan from two tomoe to three tomoe after gaining the eye.

The Sharingan itself contains three tomoe (comma). A higher mastery of the Sharingan can be seen in the creation of a new tomoe in the eye, with three tomoe being the typical highest form of the eye. The rare Mangekyou form is a unique evolution of the Sharingan beyond the three tomoe form, please see its entry for more information. An eye possessing two tomoe can allow the Uchiha clan member to track the movement of an opponent and do some minor copying of an opponents attack. For avoiding incoming attacks, the Uchiha's speed and agility will greatly control whether they can move to avoid it. However, three tomoe will greatly help in this area.

Two tomoe will also allow the ninja to pierce Genjutsu and see the surrounding reality for what it really is. It can also allow the member to pierce another’s body and see their chakra. While the eye is not refined enough to see the tenketsu and chakra circulatory system like the Byakugan, it can view the movement and flow of chakra. This can help them tell if a person is trapped in a Genjutsu, or if an attacker is a real threat or merely a bunshin.

An eye containing three tomoe will allow the ninja to see the image of an attacker’s next move from the slightest muscle tension in their body. This prevents wasteful movement and allows the Uchiha clan member to conserve much needed chakra in battle. It allows them to synchronize their movement to strike at an area moments before their opponent is even in that spot, essentially allowing them to strike out and hit their opponent before they're even there.

Three tomoe also grants the Uchiha the ability to do Genjutsu and hypnosis after locking eyes with an enemy. This can be used to cause their opponent to do an attack of the Uchiha's choosing. This hypnosis can also be used as a Genjutsu counter, which is the ability to turn a Genjutsu spell back upon the original caster without the requirement of forming any handseals.

Mangekyou Sharingan - Kaleidoscope Copying Wheel Eye (Uchiha Clan)
Sharingan is the blood inheritance limit of the Uchiha Clan. The Mangekyou Sharingan is a legendary doujutsu ability which has only emerged in a few clan members in its history. There is still mystery surrounding the eye and the Uchiha clan itself. Each user develops their own unique looking Mangekyou. The requirements for gaining the Mangekyou are very controversial in nature. After Uchiha Itachi murdered his best friend Shisui he gained Mangekyou. He told his younger brother Sasuke that to gain the Mangekyou, he too would have to kill his closest friend. Itachi told Sasuke that a scroll in their clan shrine revealed the true original purpose of the clan doujutsu. This scroll and Itachi himself revealed that the former leader of their clan, Uchiha Madara and his younger brother were the first to obtain Mangekyou. Madara himself did this by killing his friend, it's assumed his brother also killed a close comrade.

Usage of the Mangekyou techniques drains quite a bit of a user’s chakra, more so than any other normal technique. Also as a result of Mangekyou usage, the bearer will slowly lose their vision. Madara lost his vision before his brother and sought to regain his power. To do so he removed his brother's eyes and made them his own. With these new eyes, his Mangekyou took on a combined appearance of his original Mangekyou and his brother's. These "Eternal" Mangekyou eyes returned his vision and gave him unbelievable strength. With this strength it was said Madara used Sharingan's normal ability to supress the Kyuubi and tame it.

Itachi originally told Sasuke that if he gained the Mangekyou, then there would be three people who could handle it. After the time skip in the series, Hatake Kakashi revealed he too had gained Mangekyou Sharingan. Later it was revealed that Uchiha Madara himself was still alive, and was the "third" user in Itachi's statement. What part, if any, that Kakashi and Uchiha Obito's eye plays has yet to be determined.