He may keep a lower profile than his cousins J.B. (No. 3) and Penny (No. 6), but this billionaire looms large here and around the world. It’s Tom who has been entrusted with keeping an eye on Hyatt, which has been the source of much of the Pritzker family wealth. It’s Tom who hands out the influential Pritzker Architecture Prize. And it’s Tom who, last November, announced a $14 million project to modernize a port in Iraq. He’s also the chairman of the Art Institute, a trustee at the University of Chicago, and an expert on China.