Born Hawaiian, Duke became a US citizen at the age of 9 (US Hawaiian Organic Act, 30 April 1900) after the USA annexed Hawaii as a colonial territory.
Another hero of the 1912 Olympics was Jim Thorpe of the USA, a mixed race athlete (typically labeled Indian or "redskin") who won both the Pentathlon & Decathlon Gold Medals.
These athletes struggled to overcome racism. Their successes helped pave the way for a brighter present day world.
The Hawaiian Gazette 12 July 1912, pg 1
Sweden's King Gustaf V (on podium) confers Duke's 100-meter Freestyle Gold
A great celebrity, Duke Kahanamoku became perhaps better known for introducing & popularizing the Hawaiian sport of surfing around the world.