With the encyclopedia of Cologne architects presented here, a life's work by Wolfram Hagspiel (May 14, 1952 - June 3, 2021) is being published posthumously that is second to none. In more than four decades, the Cologne art historian, architectural historian and monument conservator has evaluated and recorded detailed information about the life and work of over 10,300 architects. Little was known about many of them. Hagspiel evaluated archive sources, gray literature and monographs. People who designed architecture from the construction industry up until the 20th century, such as master builders, master bricklayers and structural engineers, were also accepted. The author, who after 45 years has left behind an extensive oeuvre on the history of Cologne's architecture, is the first to provide an overview of the people who have made and have made the city a creative experience for centuries.