Andre Agassi was the number 1 tennis player in the world at one point.
Andre Agassi . Agassi returned to World No. 1 in 1999 and enjoyed the most successful run of his career over the next four years . The ATP Rankings are the Association of Tennis Professionals ' ( ATP ) merit-based method for determining the rankings in men 's tennis . The top-ranked player is the player who , over the previous 52 weeks , has garnered the most ATP ranking points .