Tricia Griffith is a rarity on two fronts: a CEO that started as an entry level employee at the company she now leads, and one of just 24 female Fortune 500 chief executives. But she’s also something else: a CEO pulling off the remarkable feat of transforming an 81-year-old company into a growth powerhouse. Progressive’s stock is up nearly 50% over the past 12 months and profits have more than doubled. In 2017, Progressive vaulted past Allstate as the nation’s third largest auto insurer behind Geico and State Farm. And perhaps most impressively, at the end of the third quarter, Progressive hit $30 billion in net premiums written after reaching $20 billion just three years earlier. Meanwhile Progressive’s one-year and annualized three-year sales growth (at 20.2% and 11.4%, respectively) tops both Apple’s and Microsoft’s. Fortune gets an inside look at how Griffith is rewriting the rules of underwriting.