The original Nicene Creed was a brief statement of faith adopted by the Church at the First Council of Nicea in 325 A.D. It was substantially revised at the First Council of Constantinople in 381 A.D. This revised version is essentially the one used today.
The rise of Constantine the Great to imperial power saw an end to Christian persecution. Constantine wanted the support of the Church but found it divided by disputes as to the nature of Christ. To put the Church on a firm footing, he called a Council at Nicea. Church leaders from throughout the Empire came together there and took on the task of making a definitive statement as to what Christians believed.