The Great Impostor is a 1961 movie based on the true story of an impostor named Ferdinand Waldo Demara.
Loosely based on Robert Crichton's 1959 biography of the same name, it stars Tony Curtis in the title role, directed by Robert Mulligan.
The film only loosely follows Demara's real-life exploits, and is much lighter in tone than the book on which it is based.
As he is arrested by the Coast Guard on an island in New England, a man born as Ferdinand Waldo Demara but known by many other identities recalls the events that brought him to this point.
Demara quit high school as a boy and joined the Army. He wanted to become an officer, but his lack of education worked against it. On a whim, he fakes a set of credentials and becomes a U.S. Marine.
When his lie is detected, Demara, facing jail, fakes a suicide and hides out as a Trappist monk. After a while, he is expelled from the monastery, captured and imprisoned in a military brig. But the warden inadvertently confides too many details...