Most Americans have never heard of the Merovingians. French schoolchildren, however, can tell you that they were the first dynasty that ruled France, starting with Clovis at the end of the fifth century.
As I discussed in an earlier post on the so-called "fall of Rome,"a number of Germanic tribes settled in the Roman Empire, including the Franks, who settled in Roman Gaul--the territory now called France in their honor. The Franks dropped their Germanic language like a hot potato, which is why modern French is a Latin-based ("Romance") language. They also quickly abandoned their paganism for Christianity.
The Merovingians were the ruling family of the Franks, so called from Meroveus, son of the sea-serpent. The story is that one of the early Frankish queens was out for a swim, got caught in a riptide, got rescued by a friendly sea monster, and decided he was totally hot. One thing led to another. Her husband the king, apparently, was cool with this.
The historical Merovingians really start with Clovis, first king of the line to convert to Christianity in 496. His wife Clotilda, already a Christian, seems to have been the major influence, though Clovis also appeared to grasp that he would be a lot more successful if Gaul's bishops supported him. There had been a lot of separate little kingdoms in what is now France, but he conquered them all. This is why he gets to be "first king of France" (481-511; there is some debate about the exact dates).
The above image is a somewhat later ivory depicting Clovis's baptism.
Clovis's descendants ruled what is now France for almost three centuries, until the last king of the line, Childeric III, was deposed by Charlemagne's father in 751, who them became king of the Franks himself. Charlemagne's court seem to have feared, after the fact, that maybe this wasn't quite as legitimate as one would have hoped. They created a determined story of Merovingian weakness and decadence (to justify the deposition), which historians then tended to believe for the next 1200 years, although recently scholars have begun rehabilitating the Merovingians.
They were certainly a violent crew, but they were also highly literate--one of them tried to introduce new letters into the Roman alphabet for sounds the alphabet didn't cover (like th)--were very supportive of the church, and did their best to be Roman. Clovis represented himself on his coins as looking like a Roman emperor and was intensely proud of being named a consul by the emperor in Constantinople. He sponsored the writing down of ancient Frankish law (called Salic law) in Latin, in imitation of Roman law.
All Frankish kings divided their kingdoms between their sons, who then all decided that Brother was the enemy. This wasn't just the Merovingians--the Carolingians, Charlemagne's dynasty, did the same thing.
Interestingly, although Charlemagne's court tried to denigrate the Merovingian dynasty, he himself named his son Louis for Clovis (take the C off Clovis and you'll see what I mean). Louis then became the most common French royal name until the monarchy finally ended in the nineteenth century.