The Agents of Ossus were a secretive group of Force-users who formed during the ascendancy of the Galactic Empire. Their founder, Jin-Lo Rayce, was a former Padawan and survivor of Order 66. They served to keep the memory of the Jedi burning in the darkness of Imperial oppression.
Fleeing Order 66 and Darth Vader's attack on the Jedi Temple, Rayce made his way first through the Coruscant underworld, then to the Core World of Chandrila. There, he set about locating any other survivors of the Great Jedi Purge. To his dismay, all he was able to locate were untrained Force-sensitives. Undaunted, he formed these adepts into secret cells, training them in the basics of Force use. He named his organization after the famous repository of Jedi knowledge, the (then) lost world of Ossus. Their purpose would be to retain the lore of the Jedi, and keep it safely hidden from the Galactic Empire.
Eschewing the lightsaber as a primary weapon, Rayce had his pupils focus on the more ubiquitous weapons of the era: blasters and vibroblades. Their Force-enhanced abilities with these weapons were impressive. They also learned how to conceal their presence, both in the Force, and visually from the seemingly omnipresent Inquisitorius. Repeated captures by Imperial agents made the group cautious and hesitant to increase their numbers by much, and the group never extended far beyond the developed Core.