Arthur is the spirit-guide Peter McGuire finds during his sweat-lodge vision; a water-spirit who becomes the personification of McGuire's own anger. If you don't believe me on this, pay attention to the water shots (starting with the opening shot of the movie), the sweat-lodge sequence, and listen carefully to almost everything Wilf says. Once you understand what Arthur is, you can see that the primary themes explored are (1) talk vs. action, and (2) if you cannot control your anger, your anger will control you. I found Ron Lea a bit too wimpy to carry off the final scene, but overall, this is a very thought-provoking movie, which I recommend to anyone who likes to think.