Gregory of Nyssa
According to Metropolitan Hierotheos (Vlachos) of Nafpaktos, an Eastern Orthodox tradition is that Gregory of Nyssa composed the section of the Niceno-Constantinopolitan Creed referring to the Holy Spirit adopted by the Second Ecumenical Council at Constantinople in 381. Siecienski doubts that Gregory of Nyssa would have endorsed the addition of the "Filioque", as later understood in the West, into the Creed, notwithstanding that Gregory of Nyssa reasoned "there is an eternal, and not simply economic, relationship of the Spirit to the Son".