Muhammad Ali.

Peter W. Kunhardt Jr., the foundation’s executive director, had known that the boxing great was seriously ill. But when he got a call from The New York Times requesting Parks’s dramatic, close-up portrait of Ali’s face, Mr. Kunhardt knew death was imminent. Indeed, by Saturday morning, the world would know that the champ had died. While many newspapers ran the image of Ali looming triumphantly over the fallen Sonny Liston, The Times ran Parks’s introspective portrait (slide #6) — two days in a row, no less.

“All the other pictures I’ve seen of Ali have been in the fight, in the moment, in the ring,” Mr. Kunhardt said. “Someone said to me, this picture is like the Mona Lisa of Ali. It’s a portrait of Gordon’s Ali. It has Ali’s essence and spirit.”

“American Champion,” which opened on Monday at the foundation’s Pleasantville, N.Y., exhibition space, features about two dozen black-and-white images — including several never seen before publicly — that Parks took of Ali between 1966 and 1970 on assignment for Life magazine. Of course, some of the images show Ali’s sleek athleticism or his personality, by turns playful and brash. Others show quieter moments at home or even in prayer. Together, they offer a well-rounded portrait of Ali taken by a photographer he grew to respect and trust.