The notoriously indignant John McEnroe won 77 singles titles in his career, including seven Grand Slams. Together with doubles and mixed doubles titles, McEnroe won 17 Grand Slam tournaments. He recorded arguably the greatest season in tennis history in 1984, when he won 96.47 percent of his matches, including Wimbledon and U.S. Open titles. (Walter Iooss Jr.(3), Steve Powell(2), Manny Millan/SI)
GALLERY: Top 20 Athletes with Irish Connections

The notoriously indignant John McEnroe won 77 singles titles in his career, including seven Grand Slams. Together with doubles and mixed doubles titles, McEnroe won 17 Grand Slam tournaments. He recorded arguably the greatest season in tennis history in 1984, when he won 96.47 percent of his matches, including Wimbledon and U.S. Open titles. (Walter Iooss Jr.(3), Steve Powell(2), Manny Millan/SI)

GALLERY: Top 20 Athletes with Irish Connections