Novak Djokovic is a Serbian right-hander widely regarded as one of the greatest players in tennis history. His return of serve and back-court defense are considered among the best ever, built on exceptional flexibility and court coverage. He holds the record for most Grand Slam singles titles won by a man, has spent more weeks at world No. 1 than any player in the Open era, and has completed the career Grand Slam multiple times over. His rivalries with Roger Federer and Rafael Nadal defined an era of men's tennis, and well into his thirties he remained a threat at the sport's biggest events.