Which god did Caesar say was most honoured by the Gauls?

According to Julius Caesar in his Commentarii de bello Gallico, the god most honoured by the Gauls was Mercury.1

Caesar described this deity as the inventor of all arts, a patron of travelers and merchants, and the most powerful figure regarding commerce and gain. While Caesar referred to the god by his Roman name, this identification is supported by numerous images and inscriptions found throughout Gaul. Scholars generally associate this figure with the Celtic god Lugus, whose influence is reflected in various place-names across Europe, such as Lyon and Leiden.1