The inscription of the Greek letters ὁ ὤν around the head of our Lord Jesus Christ in icons can be seen in Orthodox Christianity as a reference both to Exodus and to Jesus’ “I Am” statements.
The letters stand for “He Who Is” or “He Who is the Existing One,” and are part of God’s statement to Moses in Exodus 3, in the Greek Septuagint ἐγώ εἰμι ὁ ὢν.
This is slightly different in emphasis than the Hebrew Masoretic text, “I Am that I Am.”
Generally, Church Fathers believed that the Angel of the Lord speaking to Moses was God the Word, which fits better perhaps with the Septuagint Greek.
This does not exclude for Orthodox Christians God the Father and God the Holy Spirit, who are God, One in Essence.
The Nicene-Constantinopolitan Creed, following its original Orthodox form, indicates that the “One God, the Father Almighty,” is Maker of Heaven and Earth, and of all things visible and invisible. Yet it adds that the “One Lord Jesus Christ, the Son of God, the Only Begotten, begotten not made, of one essence with the Father, by Whom all things were made,” indicating that while God the Father is Maker of all things, it was by our Lord Jesus Christ that all things were made. The Creed later states that the Holy Spirit is “the Lord, the giver of life,” proceeding from the Father and worshipped with the Father and the Son, “Who spake by the Prophets.”
Our Lord Jesus Christ seems particularly identified, but always with the Trinity as a whole, as the special agent for Creation, and as Incarnate Lord “He Who Be’s,” in effect.
At the same time the Holy Spirit waters the Creation, as one liturgical hymn puts it, especially identified with the uncreated energies that, while from the Holy Trinity, come in particular from the Spirit in the Church, the Body of Christ.
The Holy Trinity is the One God, as is the Son, while the One God is the Father from Whom the Son is begotten before all ages, and from Whom the Holy Spirit likewise proceeds from all ages, All being One in essence, and All being God.
The Son, in what could be called using a Christian existentialist approach, is “He Who Is,” and in John 8 declares Himself the “I Am” of the Old Testament fulfilled in full personhood in the New.