In the 1970s and early ’80s, through experiments with lines and voids, Willis developed a signature style that brought him international attention. He called it "the wedge." Predicated on the relationship between figure and ground, a tension that Willis built up in his edging and color choice, these haunting images could resemble a curtain or a mountain peak, a threshold or a monolith. Wedges such as "Bisby" (1977) found an eager market. Collectors and dealers ranging from Larry Gagosian to Charles Saatchi to Sidney Janis to Jackie Onassis (who called Willis "Maestro") scrambled to the studio and galleries to buy them.

At the time, Serra advised, "Just keep doing the same thing, Thornton. Just keep doing the same thing," Willis recalls. But at the height of his fame, Willis felt he had exhausted his motif. He abandoned the wedge. He gave up figure-ground paintings. With work in the Museum of Modern Art, the Whitney and the Guggenheim, he in fact gave up painting entirely.

When Willis returned to painting in the late 1980s, his market had moved on. But Willis brought with him a new focus on Cubism and new interests. "I was reading about quantum physics, how everything is absolutely saturated with matter. With the figure-ground paintings there was the idea of negative-positive space. But in quantum physics I realized that everything is filled. There is no such thing as negative space. This influenced my own thinking about painted space. My paintings became areas of energy bouncing off each other. Cubism seemed to have that in it already."

Triangles and facets filled his canvases. Work such as "Gray Harmony" (1993) featured regimented designs of quiet beauty. Then came 9/11, and that changed everything. "The first plane went right over our house. I said, ‘That plane was really low.’ I listened. Kept listening. Then I heard something go ‘snap’ and I went to the fire escape. All day, refugees were streaming up the street. People crying. People covered in soot and ash. I went out onto the street and watched the towers come down."

In shock, Willis did not work for six weeks. Then one morning he got on the other side of it. "I just started to draw," he says. In three hours, he created his first painting after the attacks: In "Cubist Painting for Vered" (2001), a work dedicated to his wife, Willis did away with measured construction. "I realized the world was taking a major change, with more uncertainty." Drips ran down the front; the painting wept.

A new urgency now fills his compositions, a tension between the structures of Cubism and the gestures of Abstract Expressionism. He says he struggles with these recent paintings. Edgy, bending and sticking out into our space, they are animated by a career in abstraction. The art critic for The New Republic, Jed Perl, has called them "wonderfully persuasive" and suggestive of "an emotional terrain at once rambunctious and saturnine ... Although Willis was always a powerful painter, he seems to me to be a far more inviting artist now."

The life of Thornton Willis is a testament to the fact that an artist at any age, in any style, can produce remarkable work. He has been chasing abstraction for 40 years, and now, once again, the art world is starting to chase him.

James Panero is the Managing Editor of The New Criterion.