Nancy Blackburn Hamon found herself at the helm of one of Texas’ great oil companies but at the time had little experience to draw upon. She had no real heirs on whom to bestow her riches after husband Jake, a Texas oilman, passed away in 1985. Instead, it would be Dallas that would benefit from her largesse, her monetary gifts helping to shape the city’s arts scene in particular. Ms. Hamon’s gifts included a $20 million donation in 1988 to fund the 140,000-square-foot Nancy and Jake L. Hamon Building at the Dallas Museum of Art and $10 million for a 200-seat recital hall at Winspear Opera House. A native of San Antonio, Ms. Hamon left her paleontology studies at the University of Texas at Austin to pursue her first marriage, which lasted only four years. After a divorce, she found work as a Hollywood dancer and actress, landing roles in a handful of 1940s movies. She spent a memorable year in Honolulu with an Army special services acting troupe in which Carl Reiner was her leading man, then returned to Texas. In 1949, she became the second wife of famed oil wildcatter Jake L. Hamon Jr. Two decades earlier, Mr. Hamon had partnered with fellow oilman Edwin B. Cox, father of Southern Methodist University business school benefactor Edwin L. Cox. Mr. Hamon’s privately held oil interests were always a matter of speculation; in the early 1980s, Fortune magazine estimated his worth at $200 million. The Hamons lost their only child, Jay, in 1984 when he fell from his high-rise apartment. The death was ruled a suicide.