doorkeeper

noun

1. The person in charge of an entryway, sometimes responsible for security in the immediate area around the entryway.

   “Near-synonyms: doorman, concierge, bouncer”

   “The manager at Carnegie Hall was told to get another usher in his stead; the doorkeeper at the theatre was warned not to admit him to the house; and Charley Edwards remorsefully promised the boy's father not to see him again.”

2. (figuratively)Someone with power to keep others out of some sphere or activity.