I can think of a number of players who have made contribution to the prosperity of the game.. but none of them has done as much for the tour as the Willam sisters. The sisters have given so much (not taken nearly as much in return) to the women's tennis. They have raised the bar and helped the sport improve in popularity as well. I just can't think of any other player who has done so much as the sisters for the sake of the sport.
I may be biased a bit since I'm a dedicated fan of them.. but anyways..
I may be biased a bit since I'm a dedicated fan of them.. but anyways..