St Dismas, St Leonard, and St Roch are the patron saints of prisoners.
Prisoner of Chillon the anti-Savoyard Genevan patriot François Bonivard (1493–1570), who was imprisoned for 6 years in the castle of Chillon; he was the subject of a poem by Byron, The Prisoner of Chillon, published in 1816.
prisoner's dilemma in game theory, a situation in which two players each have two options whose outcome depends crucially on the simultaneous choice made by the other, often formulated in terms of two prisoners separately deciding whether to confess to a crime.
prisoner's friend in the armed services, an officer who represents a defendant at a court martial; the term is recorded from the early 20th century.
take no prisoners be ruthlessly aggressive or uncompromising in the pursuit of one's objectives. (The origin is military, implying that enemies were to be killed rather than captured.)
See also prisoner of conscience.