Thomas Mario Haas (German pronunciation: ; born 3 April 1978) is a German former professional tennis player. He competed on the ATP Tour from 1996 to 2017. After breaking into the world top 100 in 1997, and reaching a career-high singles ranking of world No. 2 in May 2002, his career was interrupted by injuries: Haas twice dropped out of the world rankings due to being unable to play for twelve months. His first period of injury saw him miss the whole of the 2003 season, and he did not return to the world's top 10 until 2007. He also missed over a year's tennis between February 2010 and June 2011, but afterwards returned to play on the tour. He returned to world No. 11 in 2013, after reaching the quarterfinals at the French Open for the first time in his career.
Haas reached the semifinals of the Australian Open three times, and in Wimbledon once. He reached the quarterfinal stage of each of the Grand Slam events. He won 15 career titles in singles, including one Masters tournament (Stuttgart) in 2001, and has a silver medal from the 2000 Summer Olympics.