All players:
     To  get  the  "Other Tennis Players" click on "Exhibition". Then,
enter  one  of  the  following  codes  and press [Enter] at the player
selection screen to unlock the corresponding player.

NED
SUI
CRO
CAN
IND
BRA
ITA
JPN 

King:
     Successfully complete the entire World Circuit.

Master:
     After  completing  the  World  Circuit, play Arcade mode with one
game  per set under the normal, hard, or very hard difficulty setting.
When you win the final, the next challenger will be Master.