For over a thousand generations the Jedi Knights were the guardians of peace and justice in the Old Republic. Before the dark times. Before the Empire. 
- --Obi-Wan Kenobi[src]
A Jedi was a member of the Jedi Order, which studied, served and used the mystical energies of the Force; more specifically, the light side of the Force. The Jedi fought for peace and justice in the Galactic Republic, often against their mortal enemies, the Sith, who studied the dark side of the Force. Although the Order was virtually destroyed with the culmination of the Clone Wars, and before that approximately 4000 years before by Darth Revan and Darth Malak, the Jedi lived on due in large part to the efforts of Luke Skywalker, who forged a New Jedi Order to defend first the New Republic, and later its successor, the Galactic Federation of Free Alliances.