Ever restless, Frank Stella dynamically shifted his work in both style and scale while defying categorical boundaries between painting and sculpture as he became one of America's most prolific artists of the past half century.

The artist, who has died at eighty-seven, rattled standards of modernist abstraction rather as Bob Dylan did those of folk music.

He moved American art away from Abstract Expressionism toward cool minimalism. His explorations of color and form were endlessly discussed and constantly on exhibit.

With his black paintings of the 1950s, he helped conceive a zero-degree form of art-making that paved the way for Minimalism.