In discussions of the greatest tennis players of all time, players who competed before the beginning of the sport's Open Era in 1968 are often neglected due to the difficulty of comparing their achievements to those who came later. Prior to the Open Era, amateur and professional players competed separately, complicating the picture of who was truly the best in the sport. The achievements of Rod Laver, however, effectively cut through these complications. Laver is the only player in the Open Era to have accomplished the greatest feat in tennis, winning all four Grand Slam tournaments in the same year, a Calendar Year Grand Slam. In fact, Laver's 1969 Calendar Year Grand Slam was his second, as he had already won all four in the same year as an amateur in 1962, and he also won all three Pro Slams as a professional in 1967. The confusion about how to rate players' success which stems from the pre-Open Era split between amateurs and professionals is thus irrelevant with respect to Rod Laver. He beat all the best amateurs as an amateur, he beat all the best professionals as a professional, and then he beat all the best of both once the Open Era started. Laver proved himself the greatest across different eras, and he should therefore be considered the greatest of all time.