HOK, formerly Hellmuth, Obata + Kassabaum and legally HOK Group, Inc., is an American design, architecture, engineering, and urban planning firm, founded in 1955. As of 2018, HOK is the largest U.S.-based architecture-engineering firm and the fourth-largest interior design firm. The firm maintains more than 1,600 professional staff across a network of 24 offices, and is active in all major architectural specialties. History Founding HOK was established in St. Louis, Missouri, in 1955. The firm's name is derived from the surnames of its three founding partners: George F. Hellmuth, Gyo Obata and George Kassabaum, all graduates of the School of Architecture at Washington University in St. Louis. The design firm started with 26 employees and its three founders. The practice's first building designs were schools in St. Louis suburbs, and St. Thomas Aquinas High School in Florissant was the first private/parochial school designed by the firm. Another prominent school they designed was the Saint Louis Priory School. Early years By the mid-1960s, the firm was winning commissions across the United States and began to open additional offices, starting with San Francisco in 1966 for the design of a library at Stanford University and Dallas in 1968 for the master planning and design of Dallas/Fort Worth International Airport. Also in 1968, HOK launched its interior design practice. HOK also expanded into Washington, D.C., after winning the commission to design the Smithsonian National Air and Space Museum. In 1973, HOK established a presence in New York by acquiring Kahn & Jacobs, designers of many New York City skyscrapers. By the 1970s, the firm was operating internationally and in 1975 the firm was named as architect of the $3.5 billion King Saud University in Riyadh, at the time the single largest building project in the world. In 1979, George Kassabaum was elected into the National Academy of Design as an Associate Academician. In 1983, HOK formed HOK Sport Venue Event, a subsidiary devoted entirely to designing sport stadiums, arenas, and convention centers, an architectural boom market at the time. In January 2009, the Board of HOK Group, Inc. and managers of HOK Sports Facilities, LLC transferred ownership of HOK Sport to leaders of that practice. The company became an independent firm, and rebranded itself as Populous. Expansion and acquisitions HOK's first office outside the US opened in Hong Kong in 1984, and the second in London in 1987, a practice that would be