Robert Morris, one of the most controversial American sculptors of the post-World War II era as a founder of Minimalism, a style of radical simplification that emerged in the 1960s and influences artists to this day, died on Wednesday in Kingston, N.Y. He was 87.

His wife, Lucile Michels Morris, said the cause was pneumonia.

Mr. Morris was one of a generation of artists who embraced the Minimalist credo, along with Donald Judd, Carl Andre, Dan Flavin and others. But while his peers continued to work within the genre’s austere limits, Mr. Morris went on to explore an astonishing variety of stylistic approaches, from scatter art, performance and earthworks to paintings and sculptures symbolizing nuclear holocaust.

His detractors, noting his tendency to borrow ideas from other artists freely, questioned his originality and authenticity. His supporters saw in him a mind too restlessly alive to the possibilities of art to be confined to any one style.

But nearly all agree that most of the major issues in art of the last half-century were highlighted in one phase or another of Mr. Morris’s prolific, mercurial career.