Itachi Uchiha

"Foolish little brother. If you want to kill me, then hate me, despise me. Run, run, and cling to life."
 * -Itachi Uchiha to Sasuke Uchiha after murdering the Uchiha clan

Sasuke Uchiha's brother, Itachi is a wanted S-class wanted criminal.

History
Itachi had everything an aspiring ninja could want. Very talented from the beginning, Itachi showed to be more than promising as he was the top rookie of the academy and he graduated in only one year at the age of seven! A year later, at the age of eight, he was able to activate the Uchiha Clans special Advanced Bloodline ability of the Sharingan, which is exceptional for one of such a young age, even his brother Sasuke could not activate this until the age of twelve. Boosted with this new ability Itachi became a Chuunin at the age of ten. Later Itachi would be a Jounin and ANBU squad leader at the age of only thirteen. Tired of being surrounded by people he considered as weak low-lives, Itachi decided to test his own strength in a sickening way. He began his evil deeds by killing his best friend Uchiha Shisui, and with this he obtained the greatest technique achievable by his bloodline, The Mangekyou Sharingan. It would be awhile before Itachi would commit his next act, when he would finally let his murderous intents take over. One night, dressed in his ANBU suit, he began the last act he would perform in Konoha for many years, the killing of his entire clan. He succeeded with no trouble at all, killing everyone including his Mother and Father, the only person he spared for twisted reasons was his little brother, Sasuke. There are many reasons why this could be, one is because he wanted his brother to live a life of suffering, tortured by the death of all whom he loved. Another is because Itachi possibly did not want to suffer the guilt of being responsible for the death of his entire clan, so he left one of them alive. Or, perhaps, Itachi wanted his brother to grow strong, strong enough so that one day he may be worth fighting, his last words to Sasuke were that he was not even worth killing. His Akatsuki partner is Kisame.

Fighting Style
The fighting style of Itachi is perhaps the most frightening of all those we have seen so far. He has mastered every aspect of the art of Ninjutsu, Genjutsu, and Taijutsu. His fighting style mainly revolves around a combination of many illusionary techniques mixed with ultra-fast moves that even an experienced Jounin such as Hatake Kakashi could barely keep up with. Itachi's Sharingan provides even more terrifying Genjutsu for him to use, and Uzumaki Naruto has experience it one too many times! But the most terrifying aspect of Itachi is his infamous Mangekyou Sharingan, the deadliest form of them all. The Mangekyou casts off a Genjutsu (Tsukiyomi) that is absolutely impossible to dispel, a technique that can completely submerge the victim in to a parallel world where time for he or she passes much slower for in an instant in the real world, 24 hours passes in this dimension, The World of the Grasping Moon, as Itachi calls it. What really makes this technique deadly however, is the fact that the user can do anything to his victim that he wants, from making him relive moments of his life, to torturing him for 72 hours at a time with the blink of an eye. The proof that this technique is so powerful lies in the fact that even Kakashi has fallen victim to it and remained broken, powerless and ill for days.