Bruce Graham, a partner at SOM Chicago who reshaped the Chicago skyline and redefined tall buildings worldwide, died on Saturday at the age of 84. Graham is best known for designing the John Hancock Center, with its distinctive X-shaped bracing, and the Willis Tower (formerly Sears), for many years the world’s tallest building.

Graham died from complications from Alzheimer’s disease, his son George told the Chicago Tribune.

At the elegant Hancock Center, completed in 1969, Graham’s innovative diagonal bracing, developed with the structural engineer Fazlur Kahn, offered stability while greatly reducing the amount of steel required to build the 100-story tower. The building was an innovative example of a mixed-use highrise, with shopping, parking, offices, residences, and a popular restaurant and viewing platform.

Earlier in his career, working with Walter Netsch, with whom he had a contentious relationship, and Kahn, Graham designed and detailed the Inland Steel building, with its glinting stainless steel facade.

After Hancock, working again with Kahn, Graham developed a system of bundled tubes, which allowed the Sears Tower to step up to 1,450 feet. Completed in 1974, it held the title of the world’s tallest until 1996, when it was eclipsed by the Petronas Towers in Malaysia. “Graham’s Sears (now Willis) Tower still endures today as a hallmark of the Chicago skyline while holding the title of the tallest building in North America. Equally, Graham’s Hancock Tower still holds its own as a lesson in not only structural efficiency, but elegant form and real mixed-use planning,” according to a statement from the Chicago-based Council on Tall Buildings and Urban Habitat.

Though he worked on dozens of projects around the world, in London, Barcelona, Seoul, Cairo, and other cities, the architecture and planning of his home city were a defining influence. “Most important was working in Chicago, which I think is still the best architectural city in the United States. It gave you direction, an overall direction,” Graham told Detlef Mertins in a 2002 interview for the SOM Journal. “There was a great tradition in architecture and a city that was perfectly planned after the big fire. It has a grid and a beach that goes all the way from Indiana to Milwaukee. The grid created a sense of direction for the people. It created neighborhoods with their own parks, their own school systems, and so on. I followed that kind of philosophy.”

Following his departure from SOM in 1989, Graham founded a new firm with his wife Jane, an interiors specialist at SOM, called Graham and Graham. He is survived by his three children, George, Lisa Graham Langlade-Demoyen, and Mara Graham Dworsky; his sister, Margaret Graham Lewis; and six grandchildren.