John III Megas Komnenos or Grand Comnenus was emperor of Trebizond from September 4, 1342, to May 3, 1344. He was a son of Emperor Michael of Trebizond and Acropolitissa, a daughter of Constantine Acropolites.
- Occupation
- ruler
- Position held
- emperor of Trebizond
- Citizenship
- Empire of Trebizond, Byzantine Empire
- Born
- 1321
- Died
- March 1362