Alberto Juantereno from Cuba won the 400m and 800m at the Montreal Olympic Games in 1976.
Tonique Williams
Yulia Nesterenko of Belarus won gold in the women's 100 meter dash at the 2004 Games in Athens in a time of 10.93 seconds.
The gold medal winner in the Women's 400m Event at the Rio 2016 Olympics was Shaunae Miller.
The country that won the gold medal in the Women's 400m Event at the Rio 2016 Olympics was the Bahamas.
Ian Thorpe won both gold medals.
Camille MuffatFrance (FRA)
Ye ShiwenChina (CHN)
Men: Jeremy Wariner, United StatesWomen: Tonique Williams-Darling, Bahamas
The country that won the gold medal in the Women's 400m Hurdles event at the Rio 2016 Olympics was the United States.
Brooke Bennett for the women and Ian Thorpe for the men. Ian was Australian and Brooke was American. Both competed in the 400 meter freestyle if that is the type of 400m you meant.
In the most recent Olympics (2012), Sun Yang of China won the gold in the 400m freestyle.