It is my memory that there was a Gaulish high-king (my title for him, not the historical one) whose title in Celtic was Brennus. But he was the only one who for the period of his reign lorded it over a united Gaul. The Romans called him by his title, Brennus, as it if was a name. Which is why now the Gaulish factioners occasionally have a son named Brennus. But, yeah. for that fleeting period Gaul was united. THen it broke up.