Spanish Prisoner

The Spanish Prisoner is a confidence trick originating by at least the early 19th century, as Eugène François Vidocq described in his memoirs. 
The scam.
In its original form, the confidence trickster tells his victim (the "mark") that he is (or is in correspondence with) a wealthy person of high estate who has been imprisoned in Spain under a false identity. Some versions had the imprisoned person being an unknown or remote relative of the mark. Supposedly the prisoner cannot reveal his identity without serious repercussions, and is relying on a friend (the confidence trickster) to raise money to secure his release. In this classic pigeon drop game archetype, the confidence trickster offers to let the mark put up some of the funds, with a promise of a greater monetary reward upon release of the prisoner plus a non-pecuniary incentive, gaining the hand of a beautiful woman represented to be the prisoner's daughter. After the mark has turned over the funds, he is informed further difficulties have arisen, and more money is needed. With such explanations, the trickster continues to press for more money until the victim is cleaned out, or declines to put up more funds.
Characteristics.
Key features of the Spanish Prisoner trick are the emphasis on secrecy and the trust the confidence trickster apparently places in the mark not to reveal the prisoner's identity or situation. The confidence trickster will typically claim to have chosen the mark carefully, based on his reputation for honesty and straight dealing, and may appear to structure the deal so that the confidence trickster's ultimate share of the reward will be distributed voluntarily by the mark.
Modern variants.
Modern variants of the Spanish Prisoner fraud include the advance-fee scam, in particular the Nigerian money transfer (or 419) scam. 