He was one of the 6 members of Teikou Middle School's elite basketball team, called the Generation of Miracles. He used to be Kuroko Tetsuya's partner or "light" (with Kuroko being the "shadow" that supported him). He also inspired Kise Ryouta to play in his second year of middle school. He used to be light, outgoing, and joked a lot - until his talent bloomed, and his talent progressed way over a normal middle schooler's level. He stood out above everyone else and crushed all his opponents. The game started to become boring to him, for there was no challenge. He started to think that nobody could ever match him, which is why he is now an arrogant, egotistic, uncaring jerk-ass bastard. A dick among dicks.
...But one of the hottest damn characters there ever was.
Currently, he is the ace of Touou Academy. He has now found his rival in Kagami Taiga, who is the new "light" to Kuroko, both in Seirin.
(I'm not going to write any more, in case someone wants to stay spoiler-free!)
"Your light is too dim." -To Kagami