Ronald Lee Ridenhour (April 6, 1946 – May 10, 1998) was an American known for having played a central role in spurring the federal investigation of the 1968 Mỹ Lai massacre in Vietnam.

After returning to the US in 1969, he wrote to President Nixon, members of his cabinet and two dozen Congressmen recounting what he had learned.

While serving in Vietnam, Ridenhour heard of the Mỹ Lai massacre from friends in the service.

A total of 26 soldiers were charged with criminal offenses, although Second Lieutenant William Calley was the only one convicted, for killing 22 villagers.

[4] According to Jonathan Glover's book, Humanity: A Moral History of the Twentieth Century (2001), Ridenhour took part in the Princeton University version of the Milgram experiment.