Which of the following players have won the 50 doubles titles in ATP tour history?

Andy Roddick
Rafael Nadal
Leander Paes
Novak Djokovik

The correct answer is C. Leander Paes.

Leander Paes is an Indian professional tennis player who has won 50 doubles titles in ATP tour history. He is the only player in history to have won a doubles title in four different decades. He has also won 10 Grand Slam doubles titles, the most by any male player in history.

Andy Roddick is an American former professional tennis player who won 32 ATP doubles titles. He never won a Grand Slam doubles title.

Rafael Nadal is a Spanish professional tennis player who has won 23 Grand Slam singles titles, the most by any male player in history. He has never won a doubles Grand Slam title.

Novak Djokovic is a Serbian professional tennis player who has won 20 Grand Slam singles titles, the second most by any male player in history. He has never won a doubles Grand Slam title.