response: I'm not sure.  Oh did you know that he was the second to complete the Career Grand Slam in singles?  Andre Agassi was the first to do so.
original_response: Andre Agassi for sure. They may have not competed at the same time but he completed the golden slam first.
history: I think Rafael Nadal is the best tennis player of all time. What do you think? Oh Nadal?  Well he's won a lot of titles, tournaments and medals. What do you think was he's best grand slam victory ever? I don't know!  I do know that he is widely considered to be the greatest clay court player ever. Who do you think is he's greatest adversary?
knowledge: He is the second male player, after Andre Agassi, to complete the singles Career Golden Slam.