gatekeeper:
(plural: ‘gatekeepers‘; pronunciation: the letter ‘g’ in this word rhymes with the letter ‘g’ in “garden” — for the right pronunciation, please click here)

a gatekeeper at a large gate
a person who guards, and opens and closes the main entrance (main gate) of a place to let people in and out, as a job;
an employee who oversees the work of other employees, especially who makes decisions on a particular project or plan;
a primary health care provider who watches over a patient’s health and refer them to a specialist, hospital or some other medical service,

a gatekeeper at a railway crossing
In the past, the main gates of a building, a large home or a bunglow, used to be very large and heavy, and the owners used to employ more than one gatekeeper to guard the gates.
In the present day usage, though the word ‘gatekeeper’ has not been used for the actual person standing at the door, it is being used for other positions, such as receptions or important members of the staff of an organisation.
Keeping the original meaning intact, the word ‘gatekeeper’ is used for several other positions and systems in business, politics, government policies, etc., for instance, the security system and personnel at an airport is called a gatekeeper because that is the place where the visitors to a country are checked and then allowed or deported depending on the immigration laws of that country.
