Steve Fox was a young British boxer enjoying his run as the world middleweight champion. Adopted at infancy, he always tried to search for his biological parents, as well as the origin of the scar on his left arm, but with no success. One day, the Mafia ordered him to throw a high-stakes match, but he instead won it. Going forward with their threat, they put a bounty on his head. Steve left England and sought refuge in the USA, but he soon realized there was no escape from the Mafia. Motivated by this realization, he sought the limelight once again, and took part on the fourth King of the Iron Fist Tournament.
After the tournament, he discovers through the Mishima Zaibatsu's data room that he was conceived through fertilization in-vitro, and that his mother is the assassin Nina Williams.
After having discovered a bit more about his mysterious past, thanks to a Hong Kong police officer named Lei Wulong, he felt disgust about it and vowed to stop the Mishima Zaibatsu from making more monsters like him. After once again taking part in the King of the Iron Fist Tournament, he found the Mishima Zaibatsu's research labs and destroyed them all, clearing his conscience.
After that set of events, he tried to reenter the world of boxing, but due to the world war between Jin Kazama's Zaibatsu and Kazuya Mishima's G Corporation, the big tournaments were cancelled. Without boxing, Steve lost his livelihood, and fell on a very unfilling life. About the same time, he received an invitation from Paul Phoenix and Marshall Law to train with them. Steve saw this as a good opportunity to experience other fighting styles and happily accepted the offer.
Tekken Tag Tournament 2
In this non-canon game, his ending appears with him training, only to him experience pain from his left scar and flashbacks from his life as an experiment of the Zaibatsu Labs. He then remembers a kind scientist who bonded with him named Emma Kliesen (who happens to be Leo Kliesen's mother). The flashback ends and Steve is seen in the present, lying in the ground, looking to a bright light and saying "Emma?"
Steve is set to appear in Tekken 7.