Gregory of Nyssa
Gregory of Nyssa (c. 335–395), younger brother of Basil the Great and one of the three Cappadocian Fathers, was a profound mystical theologian. His Life of Moses and On the Making of Man trace the soul’s endless ascent into God, and his defence of the full deity of the Spirit helped secure the Nicene faith at the Council of Constantinople (381).
The most speculative of the Cappadocians, Gregory read Scripture as a ladder of unending ascent: his Life of Moses takes the exodus narrative as a map of the soul's perpetual progress (epektasis) into the infinite God, and his On the Making of Man expounds humanity as the image of God from Genesis 1:26. His defence of the Spirit's deity helped secure the final Nicene settlement at the Council of Constantinople in 381.