Bill Valentine, the architect who spent half a century shaping the global design firm HOK and who pressed his profession toward sustainability long before it became fashionable, died on June 25, 2026, at his home in Mill Valley, California. He was 88.

A North Carolina native, Valentine earned a Bachelor of Architecture from North Carolina State University and a Master of Architecture from Harvard University, where he would later return as a lecturer at the Graduate School of Design. He joined HOK in St. Louis in 1962 and, in 1970, moved west to help open the firm's San Francisco office, the studio that became the center of his life's work. As HOK recounted, he rose to become the firm's president and design principal in 2000 and its chairman in 2005, retiring in 2012 after 50 years and remaining chairman emeritus for the rest of his life.

Across those decades he gave form to buildings that reshaped skylines and the way people work. In San Francisco he designed Levi's Plaza, completed in 1982, and the Moscone Convention Center, drawing on the warmth and ease of everyday materials. Abroad, he led the design of King Khalid International Airport in Riyadh, a project he later revisited in a recorded talk for HOK's design archive. His commissions grew to include research and corporate campuses for Apple, Microsoft, Adobe and Biogen, along with civic work such as the Phoenix Municipal Courthouse and the Wellmark headquarters in Des Moines.

What distinguished Valentine was less any single landmark than a way of thinking about the work. He defined good design as "a simple idea, elegantly executed and inspiring, with social significance and in harmony with the environment," a credo he carried into a sustained, sometimes evangelical, campaign for greener building. He guided HOK to adopt environmental responsibility as a core value in the 1990s and helped produce The HOK Guidebook to Sustainable Design, arguing that building less could itself be the most powerful green act. A Fellow of the American Institute of Architects and a LEED-credentialed professional, he became one of the profession's most visible advocates for low-carbon, resource-conscious design.

Colleagues remembered a leader whose warmth matched his rigor. "Bill brought a lightness to the work that belied how seriously he took it," said Eli Hoisington, co-CEO of HOK, recalling a mentor who treated architecture as a way to help people rather than to display the designer. Valentine married Jane Dorward, his wife of more than six decades, who died in 2022. He was survived by their three children and six grandchildren.

Bill Valentine leaves behind far more than the airports, plazas and campuses that carry his hand. He leaves a discipline nudged, building by building and argument by argument, toward the conviction that good architecture answers to people and to the planet at once. For the generation of architects who came up inside HOK and well beyond it, his patient half-century of insistence that design should do good, and do less harm, remains the truest measure of all that he built.