Very fascinating. I think it is Mark Landis that you have in mind:

"It obviously isn't a crime to give a picture to a museum, and they treated me like royalty. One thing led to another, and I kept doing it for 30 years," says Mark Landis, one of the most prolific art forgers in US history.

- America's most generous con artist http://www.bbc.com/news/magazine-31818367

I think this would make a really good film. An artist who is clever, talented, persuasive, calculating, and just want to do some good by donating 'forged' art to museums.