The Uchiha Clan
The Uchiha Clan, being direct descendants of the Older son of the Sage, were regarded as one of the most powerful clan in the NarutoVerse, with only the Senju Clan being strong enough to be considered their equals. Their strength stemmed mainly from their powerful Chakra, and of course, their Dōjutsu, the Sharingan.
After their continuous fights with the Senju clan, the Uchiha clan's power ultimately started to decrease. Under the guidance of Hashirama Senju, the Senju clan managed to gain the upper hand against the Uchiha, who were lead by Uchiha Madara at the time. After some time had passed, some members of the Uchiha clan had even started to defect over to the Senju clan, and around that time, Uchiha Madara decided to confront Hashirama Senju, using his newly evolved Eternal Mangekyō Sharingan, which he had gained after implanting the eyes of his dead brother Izuna into himself, after Izuna was killed by Tobirama, Hashirama's brother. After a long fight with Hashirama, Madara was finally defeated, but instead of doing what his brother wanted to do, Hashirama spared Madara, in order to try and establish peace between the two clans. At first, Madara denied, but finally agreed after witnessing Hashirama's attempt to sacrifice himself in order to bring end to the war between the two clans. And so peace was established, and the Village Hidden in the Leaf was created, with Hashirama taking on the role of Hokage.
However, this peace could not go on forever. Madara's hatred of the Senju was simply too strong, which resulted in him suspecting the Senju to betray their treaty and suppress his clan. (Which later happened) He tried to get his fellow clan members to rise against the Senju alongside him, but when not a single one of them listened, he decided to defect from the village, leaving it forever. Later on, he sought out the Nine Tailed Demon fox and took over his powers, and challenged Hashirama to an all out battle, which he ended up losing. (Although his main goal in that fight was to gain a portion of Hashirama's DNA, which he succeeded in doing.) Madara, having somehow survived the fight without Hashirama noticing, went into hiding, where he kept himself for a long time, with the world assuming that the Uchiha had been killed by Hashirama.
After the two's fight, Hashirama returned to the village, where he reigned as Hokage for some time, until the time of his death, where Tobirama took the role of the village leader. Due to not trusting the Uchiha, Tobirama decided to force them to live in their own corner of the village, having them take on the role as police officers. While on the outside it looked like he was doing this out of respect for the Uchiha and their power, the real reason for this was to be able to look after them, in order to prevent another Madara from appearing. The Uchiha however, realized this, and decided to stage a Coup d'etat, to which the village reacted to by having them all slaughtered by Itachi Uchiha, with the only exception being Itachi's brother, Sasuke.
After this, the Uchiha's reign as a supreme clan had seemingly come to an end. Itachi went on to join the Akatsuki, Madara's death had already taken place, with him leaving his plans to Obito who created the Akatsuki, and Sasuke growing up in the village as the sole survivor of the village still loyal to Konoha. Itachi's death later on left the clan with only two survivors left, Obito, and Sasuke. (And Edo Madara, if he counts)
___________________________________________
The Sharingan
The Uchiha's eyes have all in all five different forms. (Six if you count the Rinnegan) When an Uchiha first awakens his Sharingan, he (Usually) starts out with a single black tomoe in each eye, which will then become two tomoe, and then three tomoe. These are the first three basic forms of the Sharingan, which all have fairly similar powers. The main powers granted by the Sharingan is the increased perceptional abilities, which allows them to read the movements of the opponent, granting them the ability to foresee the opponents attacks and movements. Another ability it grants is the ability to see Chakra with their bare eyes, going so far as even noticing the color of the Chakra, allowing it's user to notice the difference between multiple Chakra. The last ability it grants if the ability to copy the moves of other opponents, an immensely useful ability. When a user first awakens the Sharingan, he has all these abilities at his disposal, although of course they require training. However, like one might assume, these abilities become greater depending on the amount of tomoe you have in your eyes, with one tomoe Sharingan being the weakest, and the three tomoe being the strongest.
However, that is not even close to being the whole story. An Uchiha can evolve their Sharingan even further by witnessing a great tragedy, which is often done through witnessing the death of a close friend, or a relative. Due to the emotional trauma, the eye of the Uchiha will evolve once again, this time into a Mangekyō Sharingan. The main powers of a Mangekyō are in most cases two, with one technique appearing in the left eye, and another in the right one. In some cases, an Uchiha will awaken a third power, which has in all cases been shown to be the Susano'o. The Mangekyō techniques introduced in the series so far are:
- The Kamui, which allows the user to warp either himself or others into a separate dimension. There are two versions of the Kamui, one which allows the user to warp things in his sight, and one which allows the user to warp himself, and the things he touches.
There are only two known users, Kakashi and Obito, and each of them has one Kamui ability. Both have been shown to be greatly proficient in using their variation of the technique.
- The Amaterasu, which spawns a flame on anything that catches the users glance, which will ignite for either seven days and seven nights, or until it has completely disintegrated it's victim.
The most proficient user of this technique is Sasuke Uchiha, namely due to his ability to use the Enton (Blaze Release) Othe known users are his brother Itachi, and presumably Madara Uchiha, since it has been stated that the Amaterasu is a requirement for the Susano'o, along with the Tsukuyomi.
- The Kotoamatsukami, the worlds strongest Genjutsu, which can completely control the victim, which has no way whatsoever of knowing that he's under a Genjutsu.
The most proficient user of this Jutsu would most likely be Shisui, the original wielder of the technique. Other known users are Danzō Shimura and Itachi Uchiha, both of which were granted the technique by utilizing Shisui's eyes.
- The Tsukuyomi, which allows the user to entrap his victim in a Genjutsu where the user can freely control time and space. The main strength of the jutsu is the fact that while it only lasts a second in the real world, it will feel like three days to the victim, once it has been mastered.
The most proficient user of this Jutsu would be Itachi Uchiha, who could freely manipulate both time and space when using this Jutsu on an opponent. Other known users might possibly be Sasuke and Madara, since like I stated above, the Tsukuyomi was stated to be a requirement for the Susano'o.
- The Susano'o, which allows the user to summon a giant warrior made out of Chakra, which can be used for both offensive and defensive purposes.
The most proficient user of this Jutsu would be Madara Uchiha, who is the only known user of the Susano'o's ultimate form, the Perfect Susano'o. Other known users are Sasuke and Itachi Uchiha.
However, the Mangekyō Sharingan has a great drawback, which lies in the simple fact that the more it's used, the more the users sight will lessen, ending up leaving him completely blind.
This however, brings us to the fifth evolution of the Sharingan, the Eternal Mangekyō Sharingan. In essence, it works the same as the Mangekyō Sharingan, aside from the simple fact that it will never fade, negating the biggest drawback of the Mangekyō itself. The Eternal Mangekyō is gained by merging an Uchiha's MS with another MS (Preferably the one of a close relative) which ends up looking like a combination of the two Mangekyō.
There is one final evolution however, which I feel that I should mention, the Rinnegan. The Rinnegan was the Dōjutsu of the Rikudō Sennin himself, and can only be gained through a combination of an Eternal Mangekyō Sharingan, and Senju DNA. (Even with the two, it takes a long time to appear) The Rinnegan's power is quite different from the power of the Sharingan itself, although it does share the features of a three tomoe Sharingan with the EMS. However, it's most notable power up is the fact that it grants it's user the ability to use all six nature types, along with granting him the ability to use the Seven Realm Jutsu, the Deva, Preta, Human, Animal, Naraka, Asura, and Outer Realms. In the case of Madara Uchiha, once he gained the Rinnegan, he could freely switch between the Rinnegan and his Mangekyō Sharingan, allowing him to utilize the power of both Dōjutsu.