Henri-Cartier Bresson

Obligatory Wikipedia link

Magnum Photos, Bresson's photojournalism company

Bresson's portfolio at Magnum Photos

This guess is badass.  For being as important to 20 century photography as he is, he is not mentioned in my college art history textbook.  Master of candid and street photography, trained as a painter, inspired by the Surrealists, friend of Gandhi and Henri Matisse, WWII POW, French resistance fighter, philanthropist.  All this and a damn good photographer.