He is the coach of the world's top players. By definition that makes him a tennis expert.
ESPN cameras cut away to this guy after every point even though he always has that same boring look on his face. Nobody gets more TV time than him.
He founded the Mouratoglou Tennis Academy in 1996 near Paris (later relocated to the outskirts of Nice), and has coached many up-and-coming players, including Marcos Baghdatis (whom he coached to the final of the 2006 Australian Open), Julia Vakulenko, Anastasia Pavlyuchenkova, Aravane Rezaï, Jérémy Chardy, Laura Robson, Yanina Wickmayer and Grigor Dimitrov.