Supervisor was a title for agents working on behalf of the Travelers to ensure the integrity of the timeline. Supervisors came from many different races and cultures before being brought to the Travelers' planet; most were assigned to deal with their own people, but similar-looking species could hide their features to blend in as needed. However, the masking technology required eight hours to recharge before it could be reactivated. (PIC: "Monsters", "Farewell")
A class 1 supervisor could order a Beta 5 computer to override previous instructions and answer the supervisor's questions. The computer would authenticate the supervisor's credentials by asking for nature of agents and details of their mission. Supervisor 194, code name Gary Seven, was a Human class 1 supervisor operating on Earth in 1968. (TOS: "Assignment: Earth")
In the early 21st century, Tallinn was a Romulan supervisor who was assigned to Earth to watch over future astronaut Renée Picard. (PIC: "Watcher", "Monsters").
After leaving Starfleet in 2370, Wesley Crusher eventually became a supervisor. Traveling across space and time, he came to 21st century Earth, where he recruited Kore Soong as a supervisor. Even though he could not guarantee she would be safe, Soong accepted his offer. (PIC: "Farewell")