Was the Christ of the New Testament the Creator in the Old Testament?

Yes, the Christ of the New Testament is the Creator in the Old Testament. Jesus of Nazareth was the manifestation in the flesh of the Creator God of Genesis 1. Christ as known in the New was the Creator of the Old, the image of the invisible, eternal God.

Les explains that many are confused about who Christ is, thinking He never amounted to anything until Bethlehem. But Jesus of Nazareth was merely the manifestation in the flesh of the Creator God of Genesis 1. Les teaches that whenever he teaches Genesis, Christ as we know Him in the New was the Creator of the Old. He adds that when Christ died, He paid the sin debt of every human being from Adam until the end of time, which He could never have done had He not been the God of glory. Jesus is the fleshly manifestation and the image of that invisible, eternal God.

Genesis 1:1

In the beginning God created the heaven and the earth.

Who was Jesus of Nazareth in relation to the God who created the world in Genesis 1?

Jesus of Nazareth was the manifestation in the flesh of the Creator God of Genesis 1. The Christ revealed in the New Testament was the Creator of the Old Testament. He is the image of the invisible, eternal God, and as the God of glory He paid sin's debt.