Who was he: Charlemagne was the King of the Franks and Emperor of the Romans. He's known as Charles I on the regnal lists of Germany, the Holy Roman Empire, and France. Charlemagne was responsible for Christianizing the Saxons and banned their Germanic paganisms. He paved the way to the Ottonian Dynasty. Charlemagne removed the Lombards from power in Italy and became the protector of the papacy. He's known as the founding father of both the German and French monarchies, as well as the father of Europe.
Charlemagne was a great administrator, despite his lack of education, and was a reformer of everything monetary, governmental, military, cultural and ecclesiastical. Charlemagne ushered in a new monetary system and had respect for and interest in learning, resulting in the Carolingian Renaissance. The Renaissance helped to establish the formation of a common European identity. Charlemagne was the first and last king to unite Western Europe since the Romans.
Charlemagne gave his children the education he had never gotten as a child, teaching his sons how to hunt, fight, and participate in other outdoor activities as well as the arts. Charlemagne's daughters were taught the arts and how to "be a woman." He did not allow his daughters to marry, possibly to prevent any cadet branches of the family from attempts to claim the throne, but he did not mind his daughters' extramarital affairs. Charlemagne even rewarded his daughters' common-law husbands and doted on his illegitimate grandchildren.
Background: It is believed that Charlemagne was born on April 2nd, 742, possibly in the area of Liége. His native language was most definitely a form of Germanic idiom, the specifics of which are unknown and greatly debated. On October 9th, 768, immediately after their father's funeral, Charlemagne and his brother Carloman went their separate ways to be proclaimed by their nobles and consecrated by their bishops as kings.
Charlemagne took Noyon and Carloman took Soissons. In 769, an Aquitainian and Gascon uprising, led by a Hunold, broke out between the borders of these two kings. Carloman refused to participate and withdrew, but Charlemagne pressed on. Hunold was forced to flee, but was turned over to Charlemagne by the Duke of Gascony, who feared Charlemagne. Hunold was put into a monastery and the subjection of Aquitaine started by Charlemagne's father was finally fully subdued by the Franks.
In 772, the ire Charlemagne inspired in the Lombards by repudiating his first wife, a Lombard, came to a head when Desiderius overtook some papal cities. The pope asked Charlemagne for help and Charlemagne came. He and his uncle overpowered the Lombards in 774 and he was crowned king of Italy.
On December 25th, 800, Charlemagne was made Holy Roman Emperor by Pope Leo III. In the official charters, Charlemagne preferred to refer to himself as "Charles, most serene Augustus crowned by God, the great, peaceful emperor ruling the Roman Empire" over the more direct Emperor of the Romans. Charlemagne took to his bed in Aachen on January 21st, 814 and died seven days later. Charlemagne was 72 and in the 47th year of his reign.