John Zizioulas
Greek Orthodox metropolitan and theologian of “being as communion”: personhood, not substance, is ultimate, and true personhood exists only in free, loving communion — the EO-native premise behind the claim that perfect love needs an eternally actual beloved.
John Zizioulas (1931–2023), Greek Orthodox metropolitan of Pergamon, argued in Being as Communion (1985) that personhood is the ultimate ontological category: to be a person is to be in free, loving communion, and God's being is personal communion — Father, Son, and Spirit — not an abstract substance that happens later to be related.
The premise Debby tests: if perfect love must be eternally actual between distinct persons, then a solitary God is deficient, and divine love itself routes to a plurality of persons. This is the EO-native version of the perfect-love argument, and the corpus treats it as load-bearing and still contested: Tuggy's dormant-disposition objection asks why an unexercised disposition to love is defective, and the Māturīdī approval-cluster (maḥabba, riḍā, walāya) is a worked alternative in which divine love is real without being reciprocal communion.
Where he sits in the program: cited alongside Branson's monarchy-of-the-Father work as the strongest EO-native statement of the communion premise — a premise the why-three case needs but has not yet shown to be necessary rather than fitting.
The mistaken everyday reading is "the Orthodox who proved love requires three." He supplied the premise's strongest statement; whether the premise is a necessary truth is the open question, and he is on the side of the argument that still has to be made.