The New Testament has one God who's name is: Father, Son and Holy Sprit.
The Old Testament has one God in three pictures: El or God as the great unapproachable power ruling the entire universe. YHWH, The Angel of the Lord who turns out to be the Lord, Michael the Prince, Messiah the Prince, the Fire that burned but did not consume the bush, The Captain of the Lord's Host, etc. which is God as personal and approachable. Then there is the Spirit of the Lord where we do not see an objective revelation as we do in the first two, but God working on the heart and leading the life through the subjective, existential situations. We have all of these as one God, and united in the term "Elohim" the singular plural.
Yes, The God of the Old Testament who's name is El, YHWH, The Spirit of God; and the one God of the New Testament who's name is God the Father, God The Son, and God the Holy Spirit is the creator of the entire universe.