minder

One who minds, tends, or watches something such as a child, a machine, or cattle; a keeper.

(Britain) A personal bodyguard.

A monitor assigned by the authorities to someone, such as a foreign visitor (to exercise control over their contacts with the populace) or a journalist or someone who is speaking to journalists (to monitor and control what they say).

(obsolete) One who is taken care of, such as a pauper child in the care of private person; a ward.