Kazuya Mishima (三島 一八 Mishima Kazuya?) is one of the main characters in the Tekken series. He appears in all of the Tekken games except Tekken 3. Though seen as the protagonist and hero of the first Tekken game, Kazuya is one of the major villains in the rest of the series. Most importantly, Kazuya is the son of Heihachi Mishima and the father of Jin Kazama. He's also the half-brother of Lars Alexandersson, the adoptive brother of Lee Chaolan, and the grandson of Jinpachi Mishima.
At five years of age, Kazuya was thrown off a cliff by his father, who claims that his son is weak and will have to survive and climb back up if he is to be his true son as well as his successor. Kazuya survives the fall, and makes a deal with the devil in order to survive solely to murder his father. In the years prior to the events of the original Tekken, Kazuya enters martial arts tournaments all over the world, becoming an undefeated champion due to the Devil Gene within him, (only Paul Phoenix ever managed a draw with him). When the first King of Iron Fist Tournament is announced, Kazuya takes the opportunity to get back at him, setting the stage for the first game.
Kazuya enters the tournament and makes it to the final against Heihachi. Apathetic towards the tournament's considerable prize money, Kazuya engages his father in a vicious, bloody battle in which Kazuya emerges victorious. Kazuya then proceeds to throw Heihachi's broken body off the same cliff Heihachi threw Kazuya off many years ago, and smiles with his revenge completed.
By the time of the second tournament, Kazuya has been the Mishima Zaibatsu's CEO for two years and engaged in much more evil actions beyond that of Heihachi Mishima. Around the same time, Kazuya hears the news that Heihachi is coming for him and to take back the Mishima Zabatsu. Kazuya announces the King of Iron Fist Tournament 2 in order to lure his foes out for the pleasure of destroying them. During the tournament, Kazuya encounters a contender, Jun Kazama, and impregnates her with his son and leaves her and his own son. Eventually, Heihachi makes it to the final round to face Kazuya, who he defeats because Kazuya's struggles (between the light in him, represented by Angel - who was brought forth after his meeting with Jun Kazama, and the darkness within him, represented by Devil). As a last resort, Kazuya transforms into his Devil form and continues the fight atop the roof of the Mishima Zaibatsu headquarters, but Heihachi still emerges victorious due to his training to take back the Mishima Zabatsu. In retribution, Heihachi throws Kazuya's body into the mouth of a volcano and escapes on a helicopter as the volcano erupts.