“With mutton-chop sideburns, a gone-fishing hat and a Ratatouille-style accent, Thierry Guetta is a character that documentary filmmakers pray for: gregarious, oddball, dogged and hungry for fame. In April, a documentary about Mr. Guetta – who’s either an overnight art-world sensation, or wholesale bogus creation – opens in New York, directed by British art-star Banksy.”