Elmyr de Hory was a superb forger. He was a struggling Hungarian artist who, in 1946, started to forge a wide array of post-impressionist artists. He created and sold over 1000 works for a total of over $60 million. Many ended up in museums, hanging alongside the real works by the same artists. In one case, one of his forgeries was authenticated by the artist he was mimicking (Kees van Dongen).
De Hory never copied individual pieces of art; instead he copied the style of famous artists.
He was eventually busted in 1968, and spent some time in jail in Spain. Nobody knows for sure how much of his work is still out there, on collectors' walls or in museums. He killed himself in 1976, shortly after participating in a documentary by Orson Welles called "F for Fake". Some of de Hory's forgeries collect high prices today, invariably more than the man's non-forged works.