There are real people with the name John Doe or Jane Doe on Earth, but why did these names become associated with an unidentified individual?
The association can be traced back to England and a British legal process that vanished more than 160 years ago called an action of ejectment. Landowners who wanted to bring action against a tenant who had defaulted would proceed with an action of ejectment to bypass the old English Common laws.
What made this process strange was the landowner would bring the action on behalf of a fictitious tenant against a fictitious person who had evicted them. The court then had to decide if the landowner was the valid owner of the property (and that the fictitious tenant wasn’t), and thus they would establish rightful ownership. This bizarre, roundabout way, allowed the landowner to avoid many technical legal procedures present during the time, and it established their rightful title to the property.
Many times, the landowners would name their fictitious plaintiff John Doe, and the defendant Richard Roe. Who are these people? No one knows where the names came from, but they may have been chosen because of their use during the time period. The first names John and Richard were in common usage, and the Doe and Roe were both references to deer. A doe is a female deer, and roe is a species of European deer which is also found in Britain. There was even a third and fourth name that was used if needed — John Stiles and Richard Miles.
Jane Doe came much later and identified an unknown or unidentified female, along with the variation, Jane Roe. A famous example where this was used was the case of Roe v. Wade in 1973. A female in a U.S. federal case can also be called Mary Major.
The names John and Jane Doe are still used to indicate an unidentified person upon their death until they are identified. Unfortunately, there aren’t any specific references to why any of these particular names were used or are used today.
So even though no one really knows who the first John or Jane Doe was, the practice of giving names to fictitious or unidentified people has gone back as far as the Romans. They used Titius and Seius as their name placeholders for unknown persons.