>Sasuke was a regular adorable ninja student with big dreams of being an excellent ninja like his elder brother. But after Itachi killed their family and screwed up his mind to "live in an unsightly way", Sasuke became cool, and calls himself an 'avenger', whose purpose in life was to kill his brother. For some obscure reason, that made all the girls at the academy fall in love with him.
>Sasuke first started to use his Sharingan when he fought against Haku with Naruto at Wave Country. His pretty eyes and body attracted the liking of Orochimaru, who wishes to take over his body after he became truly strong. To show his admiration, Orochimaru left a cursed seal after delightfully sinking his fangs into Sasuke's neck, which Kakashi sealed, but threatens to unleash everytime Sasuke gets excited in a fight.
>After engaging in a precarious fight with Naruto, Sasuke felt inferior as he seemed not to be improving as much as Naruto. Orochimaru took the chance to send the Sound 4 ninjas to convince Sasuke to leave the Leaf village to seek more power from Orochimaru. Thus, Sasuke abandoned Konoha (Sakura's endless whining might have helped him decide to leave in a hurry) and is on his way to the Sound village.

>Graduated from the Ninja academy at age 7 with top grades, mastered the Sharingan at age 8, became a Chuunin at age 10, Anbu leader at age 12, wiped out his entire clan and promoted to S-class missing nin at age 13.

>Top member of secret society Akatsuki, who even Orochimaru admits is stronger than himself, Itachi is shrouded with mystery. He killed his whole family with the reason that it was to measure his strength. He left his little brother alive after screwing up his mind. Although it seemed that Itachi spared his brother so he could become stronger and thus a worthy opponent someday, we believe that somewhere deep in his very disturbed heart, he loves Sasuke in his own very weird fashion.

>From someone who killed his whole family, Itachi is surprisingly unconfrontational and unbloodthirsty unlike how one would expect him to be. There were many incidents when he could have easily killed an adversary but instead left them heavily wounded and avoided as many fights as he could. Itachi has issues and it would be delightful when we finally find out why.