Who helped a catholic pope defend rome the king of the frankish empire was crowned as head of the lands called the?

The King of the Frankish Empire who helped a Catholic pope defend Rome was Charlemagne. In 800 AD, he was crowned by Pope Leo III as Emperor of the Romans, marking the revival of the title in the West and establishing the groundwork for what would later be known as the Holy Roman Empire. This alliance between the papacy and Charlemagne significantly strengthened the church's influence and the political power of the Frankish Empire.