OMAHA, Neb.—Billionaire Walter Scott, the past top executive of Peter Kiewit Sons Inc. construction firm who helped oversee Warren Buffett’s conglomerate and donated to various causes, particularly construction projects around Omaha, has died. He was 90. The Suzanne and Walter Scott Foundation that Scott founded said Scott died Saturday. The foundation did not mention a cause of death. Scott served as a board member of Buffett’s Berkshire Hathaway conglomerate from 1988 until his death, and even invested alongside Berkshire in the company’s utility and energy unit. Scott held about 8 percent of Berkshire Hathaway Energy’s stock and 105 Class A Berkshire shares with Buffett’s Berkshire holding nearly all the rest. Scott, who grew up during the Great Depression after being born in Omaha in 1931, spent his entire career working for the Peter Kiewit Sons’ Inc.—the Omaha-based construction company, which builds major projects all over the world. He worked his way …