I find this story so touching, so here it is.

Mark Landis is arguably one of the most prolific art forgers in U.S. history, having tricked over 60 museums in 20 states into believing his masterfully created replicas are authentic artworks. The catch: so far, it appears Landis, who has been diagnosed as schizophrenic but might in fact rather/also be bipolar as the New Yorker article below and the whole story suggests, has yet to commit a crime. Instead, he enjoys the performative act of pretending to be a philanthropist who makes donations of obscure artwork to art institutions, many of which unknowingly exhibited the fakes, allowing Landis the secret thrill of seeing his work on display.
Landis would often arrive at the museums dressed as a Jesuit priest with elaborate stories of how he had acquired the artworks he subsequently donated. While he’s caused headaches, confusion, and multi-year investigations, he has never sought to benefit or profit from his forgeries in any way. Instead he seemed to gain enough satisfaction from fooling curatorial staff members at various institutions.
Last year curators Matthew Leininger and Aaron Cowan collected some 90 forged artworks by Landis, as well as his “Jesuit father” costume (donated by the forger himself) and held an exhibition called Faux Real at the Dorothy W. and C. Lawson Reed Jr. Gallery in Cincinnati.*

'Art and Craft - What's it take to catch a fake' a feature documentary about him is about to be released and here's an interview with him and the makers of the film plus the trailer and another little clip:

I find it great that there is no law which would punish fooling people by the way!

He's been written about a lot - here's a quite extensive article: The Giveaway - The New Yorker

*I pretty much just quoted and modified, hence the rather nice English...