Novak Djokovic is a Serbian professional tennis player. He is currently ranked world No. 1 by the Association of Tennis Professionals (ATP). He has been ranked world No. 1 for a record total 367 weeks, and has finished as the year-end No. 1 a record seven times. He has won 20 Grand Slam men's singles titles, including a record nine Australian Open titles. Overall, he has won 86 ATP singles titles, including a record 37 Masters events. Djokovic is the only man to complete a non-calendar year Grand Slam and the first man in the Open Era to achieve a double career Grand Slam. He is also the only player to complete the career Golden Masters on the ATP Tour, which he has done twice.