William Leonard Pereira (April 25, 1909 – November 13, 1985) was an American architect. Born in Chicago, Illinois, Pereira graduated from the School of Architecture at the University of Illinois. He had some of his earliest architectural experience helping to draft the master plan for the 1933 Chicago World´s Fair. With his brother, Hal Pereira, he designed the Esquire Theater at 58 East Oak Street. In the 1930s, he moved to Los Angeles. After working as a solo architect, Pereira was hired by the Motion Picture Relief Fund and designed the first buildings for the Motion Picture Country House in Woodland Hills, California. Pereira also worked as a Hollywood art director. He shared an Academy Award for Best Special Effects for the action/adventure film Reap the Wild Wind (1942). He was the art director for "This Gun for Hire", production designer of "Jane Eyre "(1944), and "Since You Went Away" (1944) . Pereira was also the producer of "Johnny Angel" (1945), and of "From This Day Forward" (1946). Much of Pereira´s style is owed to his longtime collaborator James Langenheim, who had created the initial design for the Theme Building at LAX.

In 1949, Pereira became professor of architecture at the University of Southern California. He then formed a partnership with fellow architect and classmate, Charles Luckman, in the early 1950s. The duo designed some of Los Angeles´s most well-known buildings, including the famed "Theme Building" at Los Angeles International Airport, in collaboration with Paul Williams and Welton Becket. He parted with Luckman in 1959 and formed "William L. Pereira & Associates." In the 1960s and 1970s, he and his team completed over 250 projects, including the master plans for the Los Angeles International Airport expansion and the master plan for the city of Irvine, California, which put his photograph on the cover of Time Magazine in September 1963. He later worked with Ian McHarg on the plan for the new town of The Woodlands, Texas. Pereira designed the campus plans of the University of Southern California, the University of California, Irvine, and Pepperdine University.

Some of the iconic structures he designed include the futuristic Theme Building at the Los Angeles International Airport (LAX), the Transamerica “Pyramid” in San Francisco, and the Central (now Geisel) Library building on the campus of the University of California, San Diego. Pereira’s visionary proposals for LAX included moving sidewalks, flight status change monitors, public address systems, and “pre-tuned receivers,” resembling today´s smart phones. By the time of his death, Pereira had over 400 projects to his name. Notable architects who learned in Pereira´s firm and the classes he taught at USC include Gin Wong, William Blurock and Frank Gehry.