On October 14th 1947 US Air Force Captain Charles "Chuck" Yeagar broke the sound barrier.
Yeagar was piloting the Bell X-1, a supersonic research plane built by Bell Aircraft. It was the first manned plane to exceed the speed of sound in level flight, reaching supersonic speed, and was the first in the US experimental X-plane series. The X-1 was an experimental rocket plane. It was not the world's first rocket plane; that honour goes to the World War II Heinkel He 176, which was the first plane solely powered by a liquid fuelled rocket, but it was the first manned plane to go supersonic.
Image: By Photo by Lt. Robert A. Hoover, user:Juloml (Own work) [Public domain], via Wikimedia Commons (commons.wikimedia.org/wiki/File:Bell_X-1_color.jpg)