Thomas Samuel Okker (nicknamed "the Flying Dutchman";[2] born 22 February 1944) is a Dutch former tennis player who was active from the mid-1960s until 1980.

[5][6] Okker's father was Jewish, and was imprisoned by the Nazis during World War II, but managed to go into hiding by assuming the papers and identity of another man.

He achieved his best result in a Grand Slam tournament at the 1968 US Open, where he competed as a registered professional player, a professional player allowed to compete for prize money but playing under the control of their national associations and eligible to play in Davis Cup.

[9] Okker reached the final after defeating Pancho Gonzales in the quarterfinal and Ken Rosewall in the semifinal.

[10] Okker was awarded the first prize money at the 1968 U.S. Open, as Ashe was still considered an amateur player rather than a registered professional.

In February 1969, Okker signed a four-year contract with the Lamar Hunt's World Championship Tennis.