Shisui Uchiha

was feared as, and was one of the most talented of the Uchiha clan.

Personality
Shisui was very devoted to the clan, and they found his suicide note of claiming to be tired of carrying out the clan's duties any further to be suspicious. This is what led everyone to suspect the note was a forgery.

Shisui was the best friend of Itachi Uchiha; in fact, Itachi thought of him as an older brother. As such, the clan entrusted Shisui to spy on a weird-acting Itachi.

Background
At some point in the past, Shisui fought with Ao. Ao retains an acute memory of Shisui's chakra and ability to control others with his Sharingan. Because of this, he recognizes that Shisui's right arm and eye were transplanted into Danzō.

About six months after joining the ANBU, Itachi began to act oddly, and Shisui was instructed by the Konoha Military Police Force to keep tabs on him. Soon afterwards Shisui was found drowned in Nakano river. Although it appeared to be a suicide, with a note bidding farewell stating that he was tired of carrying out the clan's duties, the police suspected Itachi had murdered him and used his Sharingan to fake the suicide note, since Shisui was very devoted to the clan, and suicide was the least likely thing Shisui would commit. Although Itachi later confirmed this, the circumstances of his death are still a mystery. After this, Danzō took Shisui's right arm and Sharingan and implanted into himself.

Abilities
Shisui was noted to be one of the most talented members of the battle-adept Uchiha clan. He has earned the nickname of "Shisui of the Body Flicker", possibly implying that he has great mastery of the Body Flicker Technique.

As a wielder of the Sharingan, Shisui possessed an apparently unique Mind-controlling Dōjutsu that allows the user to control the mind of the target in the most discreet manner, and this is a Dōjutsu of the highest caliber. Danzō would later gain this technique when he stole Shisui's eye.

Trivia

 * Shisui's name has two interpretable meanings. Combining the words and, Shisui would mean "death water", which is a reference to his death by drowning. "Shisui" alone means "'still water'" or "'stagnant water'".