A few days ago, we noted that St. Thomas Aquinas identified the name most proper (i.e. unique) name of God as Qui Est or "He-Who-Is" (see post: ‘Qui Est’ as God’s Most Proper Name in Thomas Aquinas). Turns out that St. Thomas Aquinas is merely repeating the insight of St. John Damascene:
It appears then that the most proper of all the names given to God is "He that is," as He Himself said in answer to Moses on the mountain, Say to the sons of Israel, "He that is" has sent me (Exodus 3:14). For He keeps all being in His own embrace , like a sea of essence infinite and unseen. Or as the holy Dionysius says, "He that is good ." For one cannot say of God that He has being in the first place and goodness in the second.
St. John Damascene, On the Orthodox Faith 1, 9