Tedryn served as a Jedi Knight many, many years before the Sith War. Tedryn was one of the few Jedi entrusted to learn the secrets of the Sith, and of the powers they possessed. Tedryn became such an esteemed Jedi Knight that he recorded his knowledge in what came to be known as the Tedryn holocron. Tedryn also included in the holocron, hidden to all but the greatest Jedi strong enough to resist the temptation, information and history of the Sith.
Tedryn's holocron was passed down through the generations of Jedi and eventually fell into the hands of Jedi Master Vodo-Siosk Baas who became its gatekeeper. One of Vodo's students, Exar Kun, tapped into Tedryn's holocron to learn of the Sith. In his service to the Jedi Knights, Tedryn recorded for future Jedi Knights, all that he had learned about the Jedi Way, and its philosophies.