Six pictures of Ernesto "Che" Guevara. I am reading a long and excellent biography of him right now--Guevara, Also Known as Che by Paco Ignacio Taibo II. A fascinating story and an excellent read.
The last picture is the one that has become the face of Che everywhere (including t-shirts, posters, etc.). Some people say it is the most famous photograph in the world. It was taken at a funeral, following the (CIA-assisted) bombing of a ship in Havana.