gatekeeper

Short definition from Wiktionary

Noun

1. 1
   A person or group who controls access to something or somebody.
2. 2
   A person who guards or monitors passage through a gate.
3. 3
   A common orange and brown butterfly with eyespots, Pyronia tithonus, of the family Nymphalidae.
4. 4
   In dissociative identity disorder, an aspect of the personality that controls access to the various identities.
5. 5
   One who gatekeeps.
6. 6
   A provider of core platform services with specific characteristics (Regulation (EU) 2022/1925 of the European Parliament and of the Council)