Probate court trials usually involve fights between heirs over minor amounts of money and property. But three Dallas lawyers used a probate case to take on the largest bank in the U.S.—and won a stunning $4 billion punitive damage award against JPMorgan Chase for mishandling an estate.

The case involved the estate of Max Hopper, a prominent information technology executive who pioneered American Airlines’ SABRE reservation system. Hopper died from a stroke in 2010 and had accrued assets worth more than $19 million during 28 years of marriage to his second wife, Jo Hopper, but died without a will.