The part about being badly beaten is true. And for most of the film they're fairly fuzzy on the reason (not that there really could be a good one) motivating the initial attack. He lives in a small town in upstate NY - which is where the attack took place. And he does lose all his memories from before the attack and have to go through a lot of physical rehabilitation afterward. Even after this he continues to have issues with fine motor skills and is clearly (and reasonably) emotionally scarred from the attack. They point out that he's booted out of the hospital and therapy at some point, clearly before he's ready (gotta love the US health care system). Prior to the attack he was an alcoholic, but (self described for what it's worth) generally not a bad guy - mainly hurting himself. After the attack he has no interest in alcohol - which seems to be the one clear positive outcome. More negatively he's unable to express himself artistically in the way he used to - clearly he was a somewhat gifted drawing artist prior. So he starts to put together increasingly elaborate doll villages and scenes/scenarios as a form of therapy.
He includes dolls within the village (Marwencol) that represent real people in his life, as well as archetypes of other sorts. The mental scenarios he writes for the villagers seem to run the gambit of fantasies for companionship (and sex) to revenge scenarios against those who attacked him. The physical level of detail he brings to it is impressive as are the complex storylines. Some of the stories/themes are sort of amusing, he initially started just with a bar owned by the character that represents him and something like 20 Barbie dolls (all modified it seems by him). The town when his personal avatar of a character "found it" only has women and one of the attractions at his bar are staged "cat fights" between the women for entertainment. He's very clear (there's even a miniature sign) pointing out the fights are staged and no one is injured. Apparently in his universe it's a popular bar attraction - the only one of it's kind in Belgium. :-) Other scenarios are clearly more therapy focused. The German SS keep coming into the town and capturing/torturing him - and he's typically saved by the village women.
He takes photos of the posed figures to archive things, though he doesn't appear very thorough about archiving the photos initially. Then someone he meets sees the beauty in what he's doing and connects him up with the art world. There's some discussion about what happens when his therapy becomes more public as art - what will that mean for him, etc. You can see a lot of the staged photos on the film's website. Seeing the photos on the big screen actually makes the film more "cinematic" than it sounds.
The pictures themselves, the "art" are really very good. I can totally see going to a show of his work. I do want to come back to their website at some point. So that really worked well. Over the course of the film we learn a lot more about the artist who reveals a lot about himself over the course of the film. Is the film part of his therapy too? If it is I hope it helps him in exchange for being so open about who he is and how the experience has affected him.
It's fairly funny at times, sad at others, and altogether fascinating. So a very good documentary and definitely worth seeing - and on a big screen if you can. For more details about the artist you can checkout the films website