Unlike many sports in which the equipment and playing environments are rigidly standardized, one of the biggest challenges facing elite tennis players is the variability in schedules and playing conditions created by the variety of different tournaments which take place across the world. Above all, the differences between playing surfaces such as grass, clay, and hard courts force players to adapt their skills and strategies if they want to see consistent success. In consideration of these challenges, one of the primary hallmarks of a truly great player is the ability to win at any tournament, on any surface, and the greatest players of all time have sought to prove themselves by winning each and every significant championships. Novak Djokovic has succeeded at this overarching goal to a greater extent than any other player. In addition to winning each of the four Grand Slam tournaments and the year-end Tour Finals championship (all multiple times, with the exception of the French Open), Djokovic is the only player to date to have won all nine of the elite Masters 1000 tournaments at least once. This latter achievement, known as the Career Golden Masters, distinguishes Djokovic from his peers as the most versatile and well-rounded champion. Djokovic has also proven his ability to beat other great players directly. He holds winning head-to-head records against both of his Big Three rivals Roger Federer and Rafael Nadal, as well as dominant records against other Grand Slam champions from his era including Andy Murray, Stan Wawrinka, and Juan Martin del Potro.