Who is Uchiha?

Uchiha is a fictional clan in "Naruto" anime series.
Members (Uchihas) of the Uchiha clan are considered to feel the deep empathy and to love more than other clans.
However, Uchihas believed that they natural ability to love is a weakness. Thus, they partly hid any signs of affection, and that in turn made them look as the most evil clan.
In fact, Uchihas experience love deep inside their hearts. Nevertheless, when an Uchiha experiences considerable emotional distress or loses intimate person (like parent, siblings, friends)
Uchiha's strong sense of love will transform into a sense of hatred towards offenders and desire to revenge.
That is the nature of the Uchiha ...

General Abilities

Uchihas are innately physically strong and have potent chakra (energy to use nature styles) since they are descendants of Otsutsuki clan.
Uchihas are renowned for their "Sharingan" that empowers their skills; the "Sharingan" type is the most powerful visual kekkei genkai.
However, Uchiha is not the strongest clan.
Senju clan is the strongest one and they are the only ones who were able to confront Uchihas.
Uchiha clan and Senju clan were always in rivalry.

What is Sharingan?

Sharingan is kekkei genkai (put simply, chakra). This chakra is produced in a brain of an Uchiha and interacts with the ophthalmic nerve that results in the unique shape of eye pattern. Sharingan provides an ability to see the chakra flow, copy techniques, see person's inner self, crearte illusions and many more dangerous abilities. Regarding the shape of the eye pattern, it is true that the eyes are the windows to the soul. That means that the more complicated eye pattern an Uchiha possess, the more he suffered ...

There is more ominous thing – Mangekyo Sharingan. Mangekyo Sharingan provides power to awaken secret techniques (and they are even more powerful) of the Uchiha Clan.
Some of those techniques are Amaterasu (black flame that does not go out until the target it burnt completely), Susanoo (impenetrable in defense and destructive in attack), Kamui (ability to teleport between dimensions) ...
To awaken Mangekyo Sharingan an Uchiha has to kill an inmate person such as friend, sibling ...
However, there is huge drawback of using Mangekyo Sharingan.
Every time an Uchiha uses Mangekyo Sharingan, his/her eyesight becomes worse ... and the Uchiha will be doomed to the fate of becoming blind (no more power of the sharingan) ...
Well ... a user of Mangekyo Sharingan can avert such fate by transplating sibling's eyes ...
That makes an Uchiha posses Eternal Mangekyo Sharingan that provides limitless power ...

Renowned Uchihas

Madara Uchiha – the strongest Uchiha and the first one to awaken Eternal Mangekyo Sharingan and Rinnegan.
Obito Uchiha – his Mangekyo Sharingan provides unique ability: Kamui. During the fight, Obito could leave an impression that physical attacks pass through him since he could transport part of his body to different dimension. Was manipulated by Madara.
Shisui Uchiha – or "Shisui the Teleporter". He was very fast ninja and possesed Kotoamatsukami, the most powerful genjutsu.
Itachi Uchiha – he could basically read a person as an open book thanks to his mastery of the Sharingan. Shusui's best friend.
Sasuke Uchiha – the second one to awaken Eternal Mangekyo Sharingan and Rinnegan. Itachi's little brother.