Who is known as the pioneer of the American skyscraper?

Louis Sullivan is often regarded as the pioneer of the American skyscraper. He emphasized the importance of architectural form following function and is famous for his phrase "form follows function." Sullivan's designs, particularly in the late 19th century, laid the groundwork for the development of the modern skyscraper, influencing architects like Frank Lloyd Wright and the Chicago School. His work, including the Wainwright Building in St. Louis, showcased the potential of steel-frame construction.