User: Who is the greatest tennis player of all time?
Assistant: This is the most debated question in tennis and it seems to have multiple answers depending on how greatness is defined. While the tennis history gave us many great players, most answers pick one of the so called big three players: Novak Djokovic, Rafael Nadal, or Roger Federer. 

If we look at the number of trophies and records, the most successful player is Novak Djokovic. The dominance achieved by Rafael Nadal on a single surface is unprecedented. Some people however argue that greatness cannot be measured in trophies and records and that Roger Federer’s game is the most elegant they’ve ever seen on court.