May 9: St Gregory Nazienzen, Class III
St Gregory Nazianus (c325-390) was Archbishop of Constantinople, and is a doctor of the Church. Known as one of the Cappadochian Fathers, he was a friend of Basil the Great with whom he lived a monastic life for a few years (in defiance of his father who wanted him to assist as a priest in his diocese), and an acquaintance of Emperor Julian the Apostate.
He wrote vigorous treatises against the Emperor's rejection of Christianity and persecution of the Church, fought Arianism, and made important contributions of Trinitarian theology in particular.
Throughout his life he swung backwards and forwards over competing calls on him to play an active role in the Church politics of the time at the instigation of his father and St Basil amongst others, and the call of the contemplative life. He played a key role in relation to the Second Ecumenical Council held at Constantinople in 381, at which he dramatically resigned from the see of Constantinople to return to Nazianus.
Pope Benedict XVI gave two General Audiences on the saint back in 2007. You can find them here: