Although Karel was inducted into the International Tennis Hall of Fame in Newport, Rhode Island, in 2006, Jan is almost totally forgotten today outside his native Czechoslovakia.

All six brothers and one sister were active in sports, a new phenomenon of that era.

Karel, the most notable of the Koželuh family, achieved his fame as one of the first professional players in tennis, soccer, and field and ice hockey.

He was the Czech national singles and doubles champion 1925-1928 as well as a quarter-finalist at Wimbledon in 1926 and 1927.

Although Karel continued to play at a top level on the professional tennis circuit until he was in his forties, Jan ended his amateur career in the mid 1930s, which many considered a mistake.