Mary is the Mother of God.
All of this was thrashed out in great detail and infallibly defined as early as the third of the twenty-one Ecumenical Councils. Mary was declared the Mother of God at the Council of Ephesus (431AD) after this was denied by Bishop Nestorius, some years earlier. It is said that when he made his statement, 'the people fled the church.' Whether this means that they stopped going to his services, or that they literally got up and ran out, is no longer clear. But the point is that this teaching was not invented by the Council: it was an affirmation of the universal belief of the time. At the next Council, the Council of Chalcedon (451AD), the doctrine of the Holy Trinity was declared. This was in response to Arius, who had denied that God the Son was 'eternally begotten of the father.'
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Mary is the daughter of the Father, the mother of the Son, and the spouse of the Holy Spirit. God the Father is the Creator of all. In that sense every human being is a son or daughter of His. God the Son was sent by God the Father into the world, and 'took flesh' of the Virgin Mary. Mary is the mother of Jesus, and Jesus is God the Son, true God and true man. In that sense Mary is the mother of God the Son, but not of the other two. The Angel Gabriel told Mary that she would conceive through the 'overshadowing' of the Power of the Holy Spirit. Thus she is the Spouse of the Holy Spirit. The prayer called the Magnificat shows her reaction to this.