The Jedi were a religious order of protectors united in their devotion to the light side of the Force. With a history dating back thousands of years before the rise of the Galactic Empire, the Jedi Knights — noted for their lightsabers (laser swords) and natural ability to harness the powers of the Force — stood as the guardians of peace and justice in the Galactic Republic. Diametrically opposed to the Jedi are the members of the Sith Order, who are committed to the study and practice of the dark side of the Force. For millennia, the Jedi were the protectors of the light against the dark of the Sith.
The Jedi Grand Temple on Coruscant once served as the hub of all Jedi activity in the galaxy. Among its many roles, Temple was the primary library of Jedi knowledge and a training school for younglings and Padawans, who learned the ways of the Force under the supervision of Jedi Masters, twelve of whom were elected to serve on the Jedi High Council — the Order's highest governing authority. The High Council's staff officers were the Grand Master, who functioned as the leader of the Order and was a title reserved for the wisest Jedi Master, and the Master of the Order, who served as the Council's appointed leader.
The Jedi Code governed the Order's way of life; therefore, every Jedi was duty-bound to observe and uphold the Code or else risk banishment from the Order's ranks. The Jedi Order, while independent, provided a defensive and supportive capacity to the Galactic Republic. During the final years of the Republic, the galaxy was beset by political instability and social unrest which, in turn, created a secessionist crisis that ultimately resulted in the formation of the Confederacy of Independent Systems. Lacking the sufficient manpower needed to protect the galaxy, the Jedi became commanders and generals in the newly-formed Grand Army of the Republic. For roughly three years they commanded armies of clone troopers in a conflict known as the Clone Wars, engaging the Confederacy's battle droid forces led by Count Dooku — a former Jedi Master — and the cybernetic warlord General Grievous. With losses rising during the Clone Wars, the Chancellor linked the Jedi to the ever-mounting failures. He determined that the Jedi were traitors and conspirators who were a threat to the Republic and banned them in BBY 19, which let to the systematic purge of the Jedi Order from the galaxy.