Acting for Two: For three, actually. In French, Pierre Tornade voiced Vitalstatistix (Abraracourcix), Phonus Balonus (Caius Bonus), and the ox merchant.
Approval of God: Despite their less-than-favorable reaction to the film overall, Goscinny and Uderzo did approve of Roger Carel's performance as Asterix (and indeed most of the voice casting, for that matter), as well as Gérard Calvi's soundtrack, and kept them all for the sequel.
Disowned Adaptation: René Goscinny and Albert Uderzo didn't even know the 1967 film was being made until a few months before release, as it was greenlit by their publisher Georges Dargaud and Belvision Studios CEO Raymond Leblanc without asking them. They did not look back fondly at it, and demanded to direct the next one, Asterix and Cleopatra, which ended up better received overall.
What Could Have Been: In addition to Asterix the Gaul, which was already made without asking Goscinny and Uderzo, Belvision Studios was making two other animated films at the same time, based on Asterix and the Golden Sickle and Asterix and the Big Fight respectively. Goscinny and Uderzo ordered to destroy the footage as they were made without consulting them (it was not possible to destroy the footage of Asterix the Gaul as it was already advertised and soon to be released), and they took over for the next project, which ended up being Asterix and Cleopatra. Part of the plot for Asterix and the Big Fight was adapted into an animated film over two decades later, titled Asterix and the Big Fight in English, albeit it was really more an adaptation of Asterix and the Soothsayer.
Other Trivia:
The film had a Companion Show, a one-hour special titled Two Romans in Gaul. It was written by Goscinny and Uderzo and broadcast on French TV as promotion prior to the film's release in 1967. The Romans and other characters were live action, Asterix and Obelix were animated, making it the first time Asterix and Obelix were animated.
