Martina Hingis was 16 years, 6 months old when she gained the #1 ranking in women's tennis in March, 1997.
I think either Boris Becker or Layton Hewitt. I think they were 17 years old.
As of December 2010, Rafael Nadal is the number 1 ranked male tennis player. As of January 2011, Caroline Wozniacki is the number 1 ranked female tennis player.
The best Swedish tennis player is probably, Robin Soderling, who stands currently ranked 5 in the world.
Pete Sampras, a professional tennis player, was ranked as the world's number 1 tennis player in 1993. He held that position for nineteen consecutive weeks.
At this time, the #1 Ranked player is Zhang Ji Ke from China
Lleyton Hewitt (currently 34th in the world).