Why do we say John Doe or...

Originally, John Doe was a sham name used to indicate any plaintiff in an action of ejectment (a legal action to regain property) in civil court. Richard Roe was the counterpart, to indicate the defendant. These fake names were used in delicate legal matters, a practice that was abolished in English law in 1852. Since then, John Doe has been used to indicate any man of unknown name, with Jane Doe used for females.