The New York Times reported Friday that Bruce J. Graham, whose integration of modernist design and sophisticated engineering in buildings like the John Hancock Center and the Sears Tower transformed the skyline of Chicago and reasserted the city’s pre-eminence as a world architectural capital, died on Saturday at his home in Hobe Sound, Fla. He was 84. Mr. Graham’s buildings gave Chicago’s downtown a strong, vivid profile. One of his most famous: the Sears Tower (now the Willis Tower). The cause was complications of Alzheimer’s disease, said his son, George.

Mr. Graham, an architect with Skidmore, Owings & Merrill from 1951 until his retirement in 1989, played a determining role in propelling Chicago forward from the protomodern city created by Daniel Burnham and Louis Sullivan in the late 19th century. His most visible legacy is the 100-story Hancock Center on North Michigan Avenue, completed in 1970, and the 110-story Sears Tower (now the Willis Tower) on the west side of the Loop, the world’s tallest building when it was completed in 1974.

“With those two skyscrapers he single-handedly put Chicago back on the map,” said Joseph Rosa, the chairman of the department of architecture and design at the Art Institute of Chicago. “Without them, Chicago architecture would have been frozen in time. They expressed the optimism in Chicago and pointed toward what the future could be.”

Downtown Chicago ­ the Loop ­ shows Mr. Graham’s fingerprints at every turn. His many projects included the innovative Inland Steel Building (1957), based on an early plan by his Skidmore colleague Walter Netsch, and the Equitable Building and Chicago Civic Center (now the Richard J. Daley Center), both completed in 1965.

In the 1980s, he added to the skyline Three First National Plaza (1981), Madison Plaza (1982), the three pink-granite towers of One Magnificent Mile (1983), and the Quaker Tower (1987). South of the Loop, he designed McCormick Place North (1986), an extension of the city’s lakefront convention center.

A power broker who had the ear of Chicago’s business leaders and politicians, Mr. Graham was heavily involved in drafting the Chicago 21 plan in 1973. It called for the transformation of Navy Pier into a recreation area, the straightening of the S curve on Lake Shore Drive and an additional rerouting of the drive to free up land for the Chicago Museum Campus, a 57-acre setting of terraced gardens and walkways for the Adler Planetarium, the Shedd Aquarium and the Field Museum. All are defining features of the city today.

Mr. Graham also designed buildings across the United States and in Hong Kong; Cairo; Barcelona, Spain; Seoul, South Korea; and elsewhere abroad. In London, he led the Skidmore team that drafted the master plan for Canary Wharf in the Docklands district and presided over the design of Broadgate, a mixed-use development near Liverpool Street Station.

His signature buildings, bold and muscular interpretations of the Miesian glass box, gave Chicago’s downtown the strong, Barrymore-like profile with which it faces the world. Buildings, he said in a 1997 interview for an oral history project at the Art Institute of Chicago, should be “clear, free of fashion and simple statements of the truth.”

Bruce John Graham was born on Dec. 1, 1925, in La Cumbre, a small town outside Cali, Colombia. His father, an international banker born in Canada, traveled widely. Within a few years the family settled in San Juan, P.R., where Bruce grew up and made a hobby of mapping the city’s slum neighborhoods.

At 15 he won a scholarship to the University of Dayton in Ohio to study engineering. It was not until he traveled to the United States, he once said, that he first saw a building over 10 stories tall.

In 1943 he enlisted in the Navy and, after training as a civil engineer and a radar technician, served in the Philippines. On returning from military service he enrolled in the University of Pennsylvania, where he earned a degree in architecture in 1948.

On graduating, he moved to Chicago and sought out Mies van der Rohe, who sent him to Holabird, Root & Burgee. There he learned to make working drawings and, after two years, joined Skidmore, Owings & Merrill, a firm on the rise, where he was made a design partner in 1960.

Mr. Graham’s engineering bent found expression not only in his buildings. “He redefined how an architectural studio operates,” Mr. Rosa of the Art Institute said. “He allowed architects and engineers to have an equal voice, and this led to innovations.”

With Fazlur Khan, Skidmore’s chief structural engineer, he came up with ways to maximize office space at minimal cost. The signature X braces and exterior columns of the Hancock Building, like the exterior stainless-steel columns of the Inland Steel Building, freed up interior space and lowered costs. The Sears Tower, renamed the Willis Tower in 2009, consists of nine mutually supporting square tubes, staggered in height, allowing two towers to rise the final 20 stories of the 110-story building.

In 1999 the Hancock Building was awarded the American Institute of Architects’ 25 Year Award, given to buildings “of enduring significance” between 25 and 35 years old.

“In the heartland we believe in a direct relationship between work and thought,” he told The New York Times in 1976. “We make real buildings; we are not abstract about life, as they are in New York.”

Mr. Graham thought big, but one of his grandest schemes came to naught. In 1980 he sat down with a team of architects to draft a plan for a 1992 World’s Fair in Chicago to match the visionary fairs of 1893 and 1933, both of which altered the cityscape by creating parks and public buildings. The plan called for a series of exhibition buildings to be constructed on the near South Side and 500 acres of lagoons and islands to be reclaimed from Lake Michigan.

With the city’s economy and government in disarray, and many community groups opposed, the project withered and finally died in 1985.

In 1989 Mr. Graham retired from Skidmore and opened the firm of Graham & Graham with his second wife, the former Jane Abend, who ran the interiors department at Skidmore. She died in 2004.

In addition to his son, George, of Manhattan, Mr. Graham is survived by a sister, Margaret Graham Lewis of Gibson Island, Md.; two daughters, Lisa Graham Langlade-Demoyen of Paris and Mara Graham Dworsky of Altadena, Calif.; and six grandchildren.

“When I was a child, my dream was to build cities,” Mr. Graham told the interviewer from the Art Institute in 1997. He was asked if that was real or a child’s fantasy. “It grew into less than a fantasy,” he said.