Who did Attila the Hun fight against at the Battle of Châlons?

The Battle of the Catalaunian Plains (or Fields), also called the Battle of Châlons or the Battle of Maurica, took place on June 20, 451 AD. The battle was between a coalition led by the Roman general Flavius Aetius and the Visigothic king Theodoric I against the Huns and their vassals commanded by their king Attila. It was one of the last major military operations of the Western Roman Empire, although Germanic foederati composed the majority of the coalition army. The battle was strategically inconclusive. The Romans stopped the Huns' attempt to establish vassals in Roman Gaul, and installed Merovech as king of the Franks. However, the Huns successfully looted and pillaged much of Gaul and crippled the military capacity of the Romans and Visigoths. The Hunnic Empire was later dismantled by a coalition of their Germanic vassals at the Battle of Nedao in 454.