And God said, Let us make man in our image, after our likeness: and let them have dominion over the fish of the sea, and over the birds of the heavens, and over the cattle, and over all the earth, and over every creeping thing that creepeth upon the earth. (ASV)
"Let us make man in our image". Note the reference to a plurality of gods: the Hebrews originally believed in the existence of many gods. For more on this topic, see the Deuteronomy 32:8 section.
The plurality speaks to the Trinity.
Example: In the New Testament -- Hebrews 1 -- both the Father and Son are presented as being God. Specifically, see verse 7. 
In Exodus 3:14,15 The same word God, as used here, identifies His Name as (YHWH) and Exodus_6:3-8 clearly shows the same (plural) God is the one and only one their ancestors worshipped. Although grammatically plural, it is understood as a singular, as is the English word 'sheep' is used contextually to mean one or many.
Edit this section to note miscellaneous facts.