He was famous for creating some great decisive moments using one of the first hand held cameras made by Leica. Before that you couldn't really take photos fast enough to capture a split second in time. His work has helped us today to capture stories while they are happening, newspapers get to capture a story as it is happening to visually describe a story. Learning about his work has made me appreciate the story that can happen in a frozen moment in the tiniest fragments of time.
Here is a great link I found brilliant while looking for some of his photographs: http://erickimphotography.com/blog/2011/08/22/10-things-henri-cartier-bresson-can-teach-you-about-street-photography/
Here are some of his photographs: