Which of the following won 19 Grand Slam single titles as a professional tennis player: Roger Federer or Jonathan Stark?
Roger Federer: Roger Federer (] ; born 8 August 1981) is a Swiss professional tennis player who is currently ranked world No. 2 in men's singles tennis by the Association of Tennis Professionals (ATP). Jonathan Stark (tennis): Jonathan Stark (born April 3, 1971) is a former professional tennis player from the United States. Jonathan Stark (tennis):  During his career he won two Grand Slam doubles titles (the 1994 French Open Men's Doubles and the 1995 Wimbledon Championships Mixed Doubles).
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