Who does the FCC presume to be the control operator of an amateur station, unless documentation to the contrary is in the station records?

The FCC holds the station licensee responsible for the proper operation of the station. By default, if the FCC inspects a station or investigates an issue, they will presume that the person whose name is on the station license was acting as the control operator. If someone else is acting as the control operator, the station licensee must keep a written record documenting who that person is and when they were in control. Without that documentation in the station records, the legal burden falls entirely on the station licensee.