A Deputy

1. One appointed as the substitute of another, and empowered to act for them, in their name or their behalf; a substitute in office

Synonyms: lieutenant, representative, delegate, vice, vicegerent

2. (mining, historical) A person employed to install and remove props, brattices, etc. and to clear gas, for the safety of the miners.
3. (France): A member of the Chamber of Deputies, formerly called Corps Législatif
4. (Ireland): a member of Dáil Éireann, or the title of a member of Dáil Éireann. (Normally capitalised in both cases)
5. (United States): a law enforcement officer who works for the county sheriff's office; a deputy sheriff or sheriff's deputy; the entry level rank in such an agency

Deputy is used in combination with the names of various executive officers, to denote an assistant empowered to act in their name; as, deputy collector, deputy marshal, deputy sheriff. In the British coal mining industry, the word referred to as a deputy overman, which was roughly akin to a foreman in other industries.

substitute

representative

legate

delegate

envoy

agent