William Leonard Pereira (April 25, 1909 – November 13, 1985) was an American architect from Chicago, Illinois, of Portuguese ancestry who was noted for his futuristic designs of landmark buildings such as the Transamerica Pyramid in San Francisco. Remarkably prolific, he worked out of Los Angeles, and was known for his love of science fiction and expensive cars, but mostly for his unmistakable style of architecture, which helped define the look of mid-20th century America.