William Zeckendorf, Sr. (June 30, 1905 – September 30, 1976) was a prominent American real estate developer. Through his development company Webb and Knapp—for which he began working in 1938 and which he purchased in 1949—he developed a significant portion of the New York City urban landscape. Architects I. M. Pei and Le Corbusier have worked for Zeckendorf on many of his projects.