Fictionalized account of Ferdinand Waldo Demara Jr., who stole or created fictional identities and worked in a variety of occupations, most quite successfully.
The story is very close to the 1961 Robert Mulligan movie "The Great Impostor," which starred Tony Curtis as Ferdinand Waldo Demara, a real-life chameleon-crook who successfully posed as -- among many other things -- a surgeon, a naval officer, a Trappist monk and even a prison warden.