John Zizioulas (; 10 January 1931 – 2 February 2023) was a Greek Orthodox bishop who served as the Metropolitan of Pergamon of the Ecumenical Patriarchate of Constantinople from 1986 until his death in 2023. He was one of the most influential Orthodox Christian theologians of the 20th and 21st centuries. Academic education and career Metropolitan John was born in Katafygio, Velventos. His education began with study at the Universities of Thessaloniki and Athens in 1950, and then a year at the Ecumenical Institute of Bossey in 1955. Between 1960 and 1964 Zizioulas did doctoral research under the Eastern Orthodox theologian Georges Florovsky (1893-1979; Chair of Eastern Church History at Harvard and a member of the Russian Orthodox Church) and was a Fellow at Dumbarton Oaks Center for Byzantine Studies. He received his doctorate in 1965 from the University of Athens. Zizioulas took up a post at the University of Athens in 1964 as Assistant Professor of Church History, and then six years later, worked as Professor of Patristics at the New College, Edinburgh from 1970 until 1973. He moved to the University of Glasgow where he held a personal chair in systematic theology for some fourteen years. In addition, Zizioulas also was a visiting Professor at the Research Institute in Systematic Theology of King's College London. In 1986, he was elected titular metropolitan of Pergamon. In the same year, he assumed a full-time academic post at Thessaloniki University's School of Theology as Professor of Dogmatics. Death Zizioulas died from COVID-19 in Athens, on 2 February 2023, at the age of 92. Theology The theological work of Metropolitan John has focused upon the twin themes of ecclesiology and theological ontology. The theology of Metropolitan John reflects the influence of Russian émigré theologians such as Nikolai Afanassieff, Vladimir Lossky and his teacher Georges Florovsky. Zizioulas has also been significantly influenced by the ascetical theology of Archimandrite Sophrony (Sakharov), founder of the Stavropegic Monastery of St John the Baptist in Essex, England. Ecclesiology Zizioulas' ecclesiology was first developed in his doctoral dissertation, subsequently published in English as Eucharist, Bishop, Church. Here Metropolitan John develops critically the eucharistic ecclesiology of Nikolai Afanassief. He accepts Afanassieff's principal contention that the Church is to be understood in terms of the Eucharist. However, he criticises Afanassief's understanding as overly congregational and insufficiently episcopal in its emphasis. Finally, Zizioulas advocates an episcopocentric understanding of Church structure, understanding