Michael Graves, one of the most prominent and prolific American architects of the latter 20th century, who designed more than 350 buildings around the world but was perhaps best known for his teakettle and pepper mill, died on Thursday at his home in Princeton, N.J. He was 80. His death was confirmed by his firm, Michael Graves & Associates, which did not specify a cause. He had been paralyzed from the waist down since 2003 as a result of a spinal cord infection.