Ordered atomic bombs to be dropped on hiroshima and nagasaki, japan, in an attempt to end wwii. winston churchill harry truman franklin roosevelt woodrow wilson

The decision to drop the atomic bomb was taken by the US president of the time since the President is also the highest military leader of the US.

The American president in 1945 was Harry Truman - so this is the correct answer. He was the president from 1945 till 1953