Eastern Orthodoxy, otherwise known as Eastern Orthodox Christianity or Byzantine Christianity, is one of the three main branches of Chalcedonian Christianity, alongside Roman Catholicism and Protestantism. Like the Pentarchy of the first millennium, the mainstream Eastern Orthodox Church is organised into autocephalous churches independent from each other. In the 21st century, the number of mainstream autocephalous churches is seventeen; there also exist autocephalous churches unrecognized by those mainstream ones. Autocephalous churches choose their own primate. Autocephalous churches can have jurisdiction (authority) over other churches, some of which have the status of "autonomous" which means they have more autonomy than simple eparchies.

God the Father is a title given to God in Christianity. In mainstream trinitarian Christianity, God the Father is regarded as the first Person of the Trinity, followed by the second person, Jesus Christ the Son, and the third person, God the Holy Spirit. Since the second century, Christian creeds included affirmation of belief in "God the Father (Almighty)", primarily in his capacity as "Father and creator of the universe".