Louis Henry Sullivan, American architect, was a key figure in the development of modern architecture; he is often called the father of the skyscraper. He was also an eloquent writer on the new style as he envisioned it. Sullivan was born in Boston. He studied at the Massachusetts Institute of Technology and then briefly in Paris. He started his practice in Chicago, together with the architect Dankmar Adler. The massive Auditorium Building, innovative in the clarity and power of its design, is the chief building of the so-called Chicago School of Architecture and a memorial to his and Adler's noteworthy collaboration; they parted company in 1894. On his own, Sullivan had already designed one of the earliest masterpieces of skyscraper architecture in the United States, the Wainwright Building in St. Louis. His next great skyscraper design was the Guaranty Building in Buffalo. Sullivan was a difficult and lonely man, beset by personal problems. In his later years, his practice dwindled, but he still created some buildings of great beauty, including many small banks in the Midwest, the Farmer's Bank at Owatonna, Minnesota, being the most famous. Sullivan was a master of ornament, although he aimed at clear forms and questioned the role of decoration. The famous slogan "form follows function," which he coined, has been variously interpreted, but it has become part of the vocabulary of modern architecture. Frank Lloyd Wright was Sullivan's assistant from 1887 to 1893 and considered him his lieber meister (dear master); he paid him eloquent tribute in his book Genius and the Mobocracy. Sullivan himself was a highly poetic and persuasive writer, above all in his Kindergarten Chats (1918) and his Autobiography of an Idea (1924).