Complex sentence: Valentino Rossi (born 16 February 1979) is an Italian professional motorcycle racer and multiple MotoGP World Champion, who is one of the most successful, with nine Grand Prix World Championships to his name--seven of which are in the premier class.
Split into simpler sentences: Valentino Rossi (born 16 February 1979) is an Italian professional motorcycle racer and multiple MotoGP World Champion. He is one of the most successful, with nine Grand Prix World Championships to his name--seven of which are in the premier class.