John Doe (n.)
fictitious plaintiff in a legal action, attested from 1768 (in Blackstone). The fictitious defendant was Richard Roe. If female, Jane Doe, Jane Roe. Replaced earlier John-a-nokes (1530s) or Jack Nokes, who usually was paired with John-a-stiles or Tom Stiles.
Also used of plaintiffs or defendants who have reason to be anonymous. By 1852, John Doe was being used for "any man whose name is not known;" Britain tended to preserve it in the narrower legal sense "name of the fictitious plaintiff in actions of ejectment." John Doe warrant attested from 1935.