The Sentinel is a Career in the Force and Destiny Core Rulebook.
Every city has its secrets, and every shining beacon of civilization has its seedy underworld. Within these shadowy depths, miscreants and malcontents prey on the helpless, committing heinous crimes and leaving misery and chaos in their wake. Most law enforcement agencies try to combat criminals without violating the very laws the agencies exist to uphold. Thus, their agents must abide by strict regulations that restrain their behavior. Even institutions that exist to uphold evil laws, such as the Empire, have codes of conduct that apply to their enforcers. The Sentinel, however, plays by their own rules.
Ahsoka Tano is an example of a Sentinel in Star Wars.