If you do not know who Banksy is here's a quick summary: He is a pseudonymous British graffiti artist, internationally famous for his graffiti or "street art" due to its powerful imagery. A quick gloss over his Wikipedia page shows many of his famous works, some of which you may have seen.
Banksy is involved in a new film that is currently being screened at limited locations. Although it indirectly serves as a documentary about Banksy the true story is about the film-maker, Thierry Guetta. Through the story of Guetta the audience is able to gain an understanding of the man as well as who Banksy is.
Personally I have not yet seen this film. However from reviews I have read and the accolades of friends I have a very small doubt that this film will be a true joy to watch. As such - if you get the chance - I'm encouraging you to go see it. And if you do, let me know how you enjoyed it.