John J. Byrne, who became an insurance industry legend by saving Geico from the brink of bankruptcy in the 1970s and averting widespread financial damage, died on Thursday at his home in Etna, N.H. He was 80.

The cause was cancer, his family said.

Mr. Byrne’s stature only grew in 1985, when he took Fireman’s Fund public in what was then the biggest initial stock offering in history. Warren E. Buffett, who made some of his billions investing in Geico at the time Mr. Byrne was hired to reverse its downward spiral, called Mr. Byrne “the Babe Ruth of insurance.”

Mr. Byrne succeeded by wielding a sharp pencil to cut costs, making cautious but wise bets and juggling many financial balls. In 2000, Forbes magazine said he “made insurance look sexy.”

“Jack Byrne has distinguished himself as one of the insurance industry’s pre-eminent general managers, most creative turnaround experts and most productive capital managers,” the Insurance Hall of Fame said when it inducted him in 2009.