Patriarch Gregory III, surnamed Mammis or Μammas, was Ecumenical Patriarch during the period 1443-1450. Few things are known about his life and his patriarchate. Not even his surname is certain, with the names Mammis or Mammas being probably mocking appellations. In the generally unreliable Chronicum Majus of George Sphrantzes, it is recorded that he came from Crete, and that his real name was Melissenos. In other works he is referred to as Melissenos-Strategopoulos.