As America’s most beloved founding father, George Washington has long been credited with having a relatively enlightened outlook on the issue of slavery. Most famously, when he died in 1799, the former president freed all 123 slaves he owned in his will. But Washington notably did not free the 153 slaves owned by his wife, all of whom remained the property of her inheritors when she died. Three years earlier, one of Martha Washington’s slaves, Ona Judge, had liberated herself, slipping out of the Executive Mansion in Philadelphia and onto a ship bound for Portsmouth, New Hampshire. Though Washington soon tracked her down and tried to get her back, Judge eluded his efforts, and would live out the rest of her days in freedom. She is featured in a new exhibition at Washington’s Virginia estate, Mount Vernon, and is the subject of a new biography published this week.