Was heißt »Unbekannter« auf Englisch?

Das Substantiv »Unbekannter« lässt sich wie folgt von Deutsch auf Englisch übersetzen:

Weibliche Wortform

How this came about is unknown.
The origin of this word is unknown.
In the audience that night, unknown to the speaker, was Alan Turing.
I should like to be very famous but to remain unknown.
Often a person fears everything unknown.
I'm re-entering unknown territory.
The oldest and strongest emotion of mankind is fear, and the oldest and strongest kind of fear is fear of the unknown.
Tom's current whereabouts are unknown.
The cause of death is unknown.
This word's origin is unknown.
An unknown man was walking to and fro along the pavement.
The cause of the fire is yet unknown.
Prevention of stillbirth is very difficult, as many causes of stillbirth remain either unknown or untreatable.
An unknown master painted both paintings around the year 1400.
The two paintings were created by an unknown master in about 1400.
Jostaberries are a hybrid cross of blackcurrant with gooseberry, and they're at least as tasty as they're unknown.
The suspect's gender is currently unknown.
The exact date of Jesus' birth is unknown.
The answer is as yet unknown.
To explain something means to describe the unknown in terms of the known.