A pioneering force in photojournalism since 1936, Life magazine and its 90 staff photographers—among them, Eliot Elisofon, Margaret Bourke-White, Alfred Eisenstaedt, and Gordon Parks—documented musicians, astronauts, leaders, and celebrities as well as tense moments of war and global turmoil. In a four-million-photo roster, Life offers online viewers a window into a different America. —E.C.