response: Oh Federer?  He won the most Grand Slam single titles for men, ever.  20 of them!
original_response: Yeah I guess Federer would be even more appropriate seeming he's won more Grand Slam titles.
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? 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. What about Federer? He and Nadal seem to be Neck and neck.
knowledge: Federer has won 20 Grand Slam singles titles, the most in history for a male player and has held the world No.