Definitions:
a person who ransoms someone or something, a person who pays a ransom; a redeemer, specifically (now frequently with capital initial) christ.

a person held as security for the payment of a ransom for a ship.

a member of the order of our lady of ransom (also called our lady of mercy), founded in the 13th century to free christians taken prisoner by the muslims; = mercedarian.

a member of the guild of our lady of ransom, founded in 1887 with the principal aim of converting england and wales to the roman catholic faith.