Louis Sullivan

The father of the modern skyscraper coined the principle "form follows function" that became the bedrock of 20th-century design thinking. Sullivan's Chicago Auditorium Building (1889) and Guaranty Building in Buffalo (1896) were the first buildings to fully exploit the steel frame as both structure and aesthetic, inventing the architectural vocabulary that made modern cities possible. He was the mentor of Frank Lloyd Wright, who called him "Lieber Meister" — Beloved Master.