The Father.
<!--<span class="stiki"></span>-->Ephesians 3:14, 15
For this cause I bow my knees unto the Father,...of whom all fatherhood in heaven and earth is named, etc.
1. Of God as the sole Principle we have said enough to you yesterday: by “enough” I mean, not what is worthy of the subject, (for to reach that is utterly impossible to mortal nature), but as much as was granted to our infirmity. I traversed also the bye-paths of the manifold error of the godless heretics: but now let us shake off their foul and soul-poisoning doctrine, and remembering what relates to them, not to our own hurt, but to our greater detestation of them, let us come back to ourselves, and receive the saving doctrines of the true Faith, connecting the dignity of Fatherhood with that of the Unity, and believing In One God the Father: for we must not only believe in one God; but this also let us devoutly receive, that He is the Father of the Only-begotten, our Lord Jesus Christ.
Source: Catechetical Lectures (New Advent)