Novak Djokovic is a Serbian professional tennis player ranked World No. 1 by the ATP and is the year-end World No. 1 for both 2011 and 2012. He is considered by many to be one of the greatest tennis players of all time. He holds several men's world records of the Open Era: becoming the youngest player in the Open Era to have reached the semifinals of all four Grand Slam events both separately and consecutively; the first and only man to win three consecutive Australian Open titles in the Open Era; and playing the longest Grand Slam men's singles final in history (5 hours 53 minutes). Djokovic's ATP tournament records include winning 31 consecutive ATP World Tour Masters 1000 series matches, playing in the finals at all nine ATP Masters 1000 tournaments (a record matched by Roger Federer), and being one of the three players (alongside Andre Agassi and Federer) to win seven.