The correct answer is Charlemagne.
Charlemagne was king of the Franks from 768, nominal king of the Lombards since 764 and emperor of the Carolingian Empire from 800 until his death.
Son of King Pepin the Short and Bertrada of Laon, succeeded his father and viceroy with his brother, Carloman I. Although relations between the two became strained, the sudden death of Carloman prevented the outbreak of war. He reinforced the friendly relations that his father had maintained with the papacy and became his protector after defeating the Lombards in Italy. He fought the Muslims who threatened their possessions in the Iberian Peninsula and tried to seize the territory, although he had to fight in retreat and because of an attack by the Basques, he lost his entire rearguard, as well as Roldán, in the Roncesvalles gorge. He fought against the Slavic peoples. After a long campaign he managed to subdue the Saxons, forcing them to convert to Christianity and integrate them into his kingdom; in this way he paved the way for the establishment of the Holy Roman Empire under the Saxon dynasty.
He expanded the different Frankish kingdoms into an empire, to which he incorporated a large part of Western and Central Europe. He conquered Italy and was crowned Imperator Augustus by Pope Leo III on December 25, 800 in Rome, thanks to the opportunity offered by the deposition of Constantine VI and what was considered the vacancy of the imperial throne, occupied by a woman, Irene. These facts provoked the indignation of the imperial court, which refused to recognize its supposed title. After a frustrated wedding plans between Charlemagne and Irene, the war broke out. Finally, in 812 Miguel I Rangabé recognized Charlemagne as emperor (although not "Emperor of the Romans").