Byline: Lori Hawkins

In 1943, Lady Bird Johnson bought a failing low-power, daytime-only Austin radio station using $17,500 from her inheritance. She wanted a financial fallback in case her husband's fledgling political career didn't work out.

Over the next several decades, her business acumen helped parlay one risky deal into multimillion-dollar holdings that included radio and TV stations, banks and real estate.

Although best known for her environmental efforts, Mrs. Johnson was an astute businesswoman who learned on the job by asking questions and listening to financial advisers who were fiercely loyal to her, former business associates said.

She ultimately became the only first lady to build a business empire with her own money and become a millionaire in her own right.

"She took a nickel-and-dime outfit and built it into a thriving media enterprise, and she loved doing it," said businessman and former Austin Mayor Roy Butler, whose own radio stations competed with Mrs. Johnson's. "She would keep big shoeboxes of invoices and checks at the ranch, and she examined and signed every one."

But the boardroom wasn't Mrs. Johnson's first calling. After she earned degrees in history and journalism from the University of Texas, her career plans included teaching or writing. Meeting Lyndon Johnson in 1934 changed that.

They married the same year, and...