Jack's personality is similar to Seto Kaiba's; he is somewhat cold-hearted, and often acts as an anti-hero. Jack is an arrogant man at the beginning of the story who thinks of his opponents as little more than entertainment for himself and his audience. However, after losing to his former friend Yusei, Jack realizes what he's been missing as King and decides on starting his own journey to becoming a real duelist. Upon meeting Carly Carmine, he realizes the error of his ways, and tries to repay Yusei and the others.
Source from Wikipeida