Since Middle School, I can remember seeing work from Matthew Brady and not even knowing it. His photos are so influential and important to the US that he is almost a photography God in my mind.
His photos during the Civil War are what catapulted him into photo stardom. They not only show the attrocities of war, but there is something so delicate of the time period that they are taken in. For me, whenever I think of anytime before 1900 it just looks very primitive in my mind. So to have photos that prove me wrong blow me away.
Also, his portraits of Lincoln are great too because these were some of the first photos that documented a living president.