Which olympic tennis player, Rennae Stubbs or Juan Martín del Potro, competed in the most Olympic games? 
Rennae Stubbs: Rennae Stubbs (born 26 March 1971) is an Australian retired tennis player. Rennae Stubbs:  She represented Australia at four successive Summer Olympic Games: Atlanta 1996, Sydney 2000, Athens 2004, and Beijing 2008. Juan Martín del Potro:  Other career highlights include winning the bronze medal in men's singles at the 2012 London Olympics and the silver medal at the 2016 Rio Olympics and being part of his country's successful Davis Cup team; but his career has also been hampered by a succession of wrist injuries.
i don't know