Alfred ("Eisie") Eisenstaedt's career as a photographer might have ended early if word had gotten around about his second professional assignment in 1930. He had been sent by a German photo agency to Assisi, Italy to cover the marriage of Princess Giovanna of Savoy to King Boris III of Bulgaria. Eisenstaedt brought 240 pounds of camera equipment, including glass-plate film, and set it up outside the church. "I was so impressed by the pageantry that I photographed like mad—street scenes, the crowds, choirboys, the church—everything except the bride and groom," says Eisenstaedt. "My editor was very perplexed, but he couldn't fire me because I was working free-lance."

Despite that mishap, Eisenstaedt, the son of a West Prussian merchant, emerged as a pioneer of the fledgling art of photojournalism. In place of the stiff, posed images that had formerly served as news pictures, Eisenstaedt, with an uncanny eye, sought a sense of immediacy and realism through candid photographs taken with available light. That approach led to a distinguished international career—he has been a photographer for LIFE since 1936 and PEOPLE since 1974—and this month Eisenstaedt is being honored with a 101-print retrospective exhibition at the National Theatre in London.

The exhibit demonstrates how Eisenstaedt, still active as a photographer at age 87, has chronicled the lives of celebrated political, literary and entertainment figures for more than half a century. The secret of his ability to deal with the pressures—and egos—is simple, says Eisenstaedt. "When I first went to Hollywood in 1938, Wilson Hicks, the picture editor of LIFE, said, 'The most important thing is not to be in awe of anyone. Remember, you are a king in your own profession.' I have never forgotten those words."