In Book 6 of his Commentaries on the Gallic War, Julius Caesar refers to a Gaulish god whom the druids believed that all the Gauls were descended from. He does not give this god's name, but (following the practice of interpretatio romana) refers to him under the name of a Roman god he deemed comparable: Dis Pater, Roman god of prosperity and of the underworld.
The identification of the god behind Caesar's description has been a long-standing subject of Celtic religious research. The most often cited candidate for "Gaulish Dis Pater" is Sucellus, a mallet wielding god of the Gauls. The arguments for this identification are largely based on iconographic parallels with mallet-wielding figures in Etruscan, Greek, and Roman mythology. Other major candidates include Taranis, the only Celtic god elsewhere identified with Dis Pater in classical literature, and Cernunnos, a Celtic god with a distinct chthonic-fertility character.
The passage in which Caesar described Gaulish Dis Pater has also been appreciated for the light it throws on Celtic date-keeping, and its innovative ethnographic methods. Greco-Roman ethnography prior to Caesar usually attempted to fit the origins of barbarian peoples into Greek mythological frameworks. Caesar broke with this in crediting, and reproducing, a native Gaulish tradition about their descent. Elias Bickerman deemed this passage a "Copernican discovery" in the history of Greco-Roman ethnography.[1]: 76