When he was 26, in 768 AD, Charlemagne became the co-ruler of the Carolingian empire, beside his brother Carloman when their father died.
And when his brother died in 771, Charlemagne became sole ruler. When he turned into king his first job was to quiet down an uprising within his country, and he was surprisingly very successful in stopping the revolt.
Later he married a Lombard princess, which made relationships with Italy stronger, but a year later he re-married which hurt the relationship with foreign countries.
Charlemagne later fought the Lombard's to help Pope Adrian 1 regain several territories that belonged to papacy. After two years, Papacy was finally captured. After he took Papacy Charlemagne was crowned with an Iron crown and the people of Papacy swore their allegiance to him. And now ruling Italy and France Charlemagne was the strongest man in Europe. There were still some revolts in Italy but by 776 AD most have been quieted down.
Charlemagne also fought the muslims, he won many battles against the muslims, so the muslims offered him a treaty but during the treaty the muslims made a surprise attack to the rearguard and killed all of them even Charlemagne nephew.Enraged he conquered the muslims.
Charlemagne was also able to expand his country, in another part of his empire, Charlemagne fought 18 battles against the Saxons in 30 years, he also forced at the Saxon to convert them into Christianity.
Charlemagne also invaded many other countries, and In 799 the Pope was again threaten and called Charlemagne to help. Charlemagne went to Rome and protected the pope, after his heroic deed the Pope crowned him the ruler of Rome.
In 813 Louis the Pious the king of Aquitaine was crowned co-emperor. At the age of 72 Charlemagne fell ill and died in 814.