All Tennis Players How Many Grand Slams Has Henry Slocum Won? Henry Warner Slocum, Jr. (May 28, 1862 – January 22, 1949) was an American male tennis player who was active in the late 19th century.Henry Slocum has won 2 Grand Slams. FacebookTwitterEmail How Many Grand Slams Has Madison Keys Won? How Many Grand Slams Has Jannik Sinner Won? How Many Majors Has John Isner Won?