The Franks were a Germanic tribe that migrated to the fertile plains of Gaul. The barbarian tribes were united under the Merovingian dynasty in the late 400s.
The first ruler, Clovis, was a rutheless warrior who conquered surrounding lands. He also had the help of the church when he converted to Orthodox Christianity. This made him King of the Franks in the eyes of the pope.
After AD 700 the Merovingians where succeeded by the Carolingians. One of the more famous was Charles the Hammer, who beat the Muslim forces in the Battle of Tours, arguably one of the most decisive battles in all of history.
One of the most notable Frankish kings was Charlemagne or Charles the Great.