Simplify the following text for a Grade 9 native English-speaking person.
Original: The Holy Roman Emperor ( , or `` Roman-German Emperor '' ) is a term used by historians to denote a medieval ruler who , as German King , had also received the title of `` Emperor of the Romans '' from the Pope . After the 16th century , this elected monarch governed the Holy Roman Empire ( later called Holy Roman Empire of the German nation ) , a Central European union of territories of the Medieval and Early Modern period .
Simplified: Holy Roman Emperor was the title that was given to the ruler of a loose group of places in what is now called Germany called the Holy Roman Empire .