Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 126; Flight Crew Total 11901; Flight Crew Type 1425
Aircraft Equipment Problem Critical
Flight Crew Landed As Precaution; Flight Crew Returned To Departure Airport
Aircraft
While in cruise at FL390; left generator failed.  We complied with QRH which directed us to reset generator.  After about 3-5 minutes; generator failed again.  APU was deferred so QRH directed us to land at nearest suitable airport.  We considered ZZZ; ZZZ1; ZZZ2; and ZZZ3.  ZZZ was closest so we returned to ZZZ and made a normal landing with one generator.
B757 Captain reported the left generator failed during cruise which resulted in an air turn back.