This work is an investigation of the writings of the famous translator of the first Spanish Bible (Biblia del Oso/Bear Bible), Casiodoro de Reina. Reina escaped with other Catholic monks from a monastery near Seville, Spain. Reina joined the Protestant Reformation. However, Reina was accused of being sympathetic to the Oneness martyr, Michael Servetus. The author traces the life of Reina and analyzes the ancient archives hitherto unknown to Oneness adherents. The archives are analyzed to determine if Reina maintained a theology of one solitary God in contrast to Trinitarian doctrine.