Novak Djokovic is a Serbian professional tennis player. He is currently ranked world No. 1 in singles by the Association of Tennis Professionals (ATP), and has held the top position for a record total 374 weeks, finishing as the year-end No. 1 an Open Era record seven times. He has won a total of 93 singles titles on the ATP Tour, comprising a joint-record 22 Grand Slam men's singles titles, a record 10 Australian Open titles, a record 38 Masters titles, a joint-record 6 Tour Finals titles, and a record 66 Big Titles. Djokovic has completed a non-calendar year Grand Slam in singles, becoming the only man in tennis history to be the reigning champion of the four majors at once across three different surfaces. He is also the first man in the Open Era to achieve a double Career Grand Slam in singles and the only player to complete the career Golden Masters in singles by winning all of the nine Masters tournaments, which he has done twice.