If we trace back to
In the beginning God created the heaven and the earth
and read the JFB commentary on the Hebrew translations, even the word God was used in the plural form.
The following is an excerpt from the commentary on Genesis 1:1
1. In the beginning--a period of remote and unknown antiquity, hid in the depths of eternal ages; and so the phrase is used in @Pr 8:22,23.
God--the name of the Supreme Being, signifying in Hebrew, "Strong," "Mighty." It is expressive of omnipotent power; and by its use here in the plural form, is obscurely taught at the opening of the Bible, a doctrine clearly revealed in other parts of it, namely, that though God is one, there is a plurality of persons in the Godhead--Father, Son, and Spirit, who were engaged in the creative work (@Pr 8:27 Joh 1:3,10 Eph 3:9 Heb 1:2 Job 26:13).
I believe when God said Let us make man in our image, "us" means God the Father, the Son and the Holy Spirit.