Compared to Guardians and Consulars, Sentinels were Jedi whom often combined the Force with more worldly skills (law, investigation, mechanical skills etc.). Although they weren't typically as martial as Jedi Guardians or Warriors, they were still capable combatants in their own right and their strengths often lied in the manner in which they fought, quick to adopt new manners of fighting styles, weapons, and even used blaster and projectile weapons. Thoughout their history prior to the destruction of the Jedi Order In lieu of Order 66, Jedi Sentinels were some of the most recognizable and accessible type of Jedi in the galaxy as they often worked in solving more small-scaled and community-oriented problems and individuals over larger political or military gains; many Sentinels took to roles such as private investigators or even acted as vigilantes from time to time to address issues created by corrupt law enforcement.
While some sources were unclear, it is believed the Sentinel discipline was founded by Jedi Master Morrit Ch'gally when he was a member of the Acquisition Division within the Army of Light.This discipline would be active for countless millenia, acting as one of the most accessible Jedi in the galaxy.
In 19 BBY shortly before the Clone Wars ended, the Jedi Order faced dissolution when Chancellor Palpatine issued Order 66; the resulting ordinance nearly exterminated all of the Jedi throughout the galaxy and much like their colleagues, Sentinels suffered substantial losses. While survivors of the discipline roamed the galaxy, many were hunted by the Galactic Empire through both ISB and Inquisitorius, the latter the most dangerous to them. Many of them would retreat into hiding or acted as vigilantes for a time in hope of restoring the Jedi Order eventually. Despite their efforts, many of them were killed by Inquisitors, Imperial officers, and often faced betrayal by individuals and communities they once protected for credits or opportunities and favors in the Empire.
In 3 BBY, with the supposed death of Ahsoka Tano, Darth Vader considered her demise to be the final act of the Great Jedi Purge. Grand Moff Wilhuff Tarkin considered Vader the last remnant of the Jedi faith, making the Sentinel discipline believed to be eradicated.