His more famous namesake took the throne of Spain after the death of Ferdinand in 1516, but didn't take his more common title until his installation as Holy Roman Emperor in 1519.  
The first monarch to bear this name and number ruled France during the Hundred Years' War, signing the Peace of Bretigny which temporarily ended hostilities with the British.  His more famous namesake took the throne of Spain after the death of Ferdinand in 1516, but didn't take his more common title until his installation as Holy Roman Emperor in 1519.  FTP give the common name and number of these monarchs, the latter of which founded the Habsburg Dynasty.
The first monarch to bear this name and number ruled France during the Hundred Years' War, signing the Peace of Bretigny which temporarily ended hostilities with the British.  
Charles V