Jin Kazama is the poster-boy of the Tekken franchise, the grandson of Heihachi Mishima, who trains him to enter the King of Iron Fist Tournament. However, when it becomes apparent that Jin possesses the so-called Devil Gene, Heihachi's allegiances shift, as he wishes to take it for himself.
Whenever Jin loses control, the Devil Gene can take over, transforming into the uber-powerful (and scary) Devil Jin. Attack-wise, he's best known for his extremely strong punches, to the extent that some have cried fowl that he has been overpowered, and as such with the release of Tekken 5, his strength was nerfed in the interest of fairness (though Devil Jin has been left untouched).
Jin's drama is the focal point of the series, his feud with both Heihachi and his father Kazuya, as well as his constant fleeting between a status of hero, anti-hero and antagonist. However, it's his enormously powerful fist attacks for which he is best remembered (to the frustration of many, I imagine).