Halt! Who goes there!

Halt! Who goes there! Is a phrase which refers to a sentry, or someone standing guard, who used to shout this at people who were approaching the gates of where they were guarding, and they did not know who this person was. It was originally used by guards of this nature but is now a cliched term for someone referring to another person approaching they do not know or recognize; it is also commonly used in stage productions.