Original: Chief Opechancanough led a coordinated series of surprise attacks of the Powhatan Confederacy that killed 347 people, a quarter of the English population of Jamestown.
Simplified: The number killed, 347, was almost one-third of the English population of Jamestown. They were killed by a number of surprise attacks by the Powhatan Confederacy (a Native American tribe), who were ruled by Chief Opechancanough.