Martin Sorrell, S4 Capital

Today's guest needs no introduction. And yet, over the past 21 months, the financial wizard who built WPP into the world's largest advertising holding company has been busy reintroducing himself as the executive chairman of S4 capital. Days before his 75th birthday, we discuss everything from what motivates him today, why the holding company model he helped create is an "albatross," what the game plan is for S4 and why he bristles at the old criticism that he is not a creative person.