The Judges were first introduced by Balthier in the game when Vaan and the sky pirate team were looking for a way out of Nalbina Dungeon:

Balthier: The self-proclaimed guardians of law and order in Archadia. They're the elite guard of House Solidor. Which effectively makes them the commanders of the Imperial army. If you ask me, they're more executioners than judges.

The Ministry of Law and the Archadian Judge System was created after House Solidor first rose to power in Archadia in 615 Old Valendian.9 Crimes and conflicts were on the rise as Archadia expanded its territories, and a military court system, which eventually evolved into the current Judge system, was introduced to reduce the time required for trials.10

In actuality, the Judges survey the movements of the military11, and although they have the authority to try alleged criminals, they are equivalent to House Solidor’s bodyguards.

There are approximately 2500 members belonging to the Order of Judges, whom of which are all elites excelling in both literary and military arts. A total of 18 outstanding members were named “Judge Magister” and command the other judges under different departments named “Bureau”.12

Judge Magister Gabranth

Gabranth is the leader of the 9th Bureau, which is responsible for information collection and dissemination in order to bring about disorder in hostile countries. Even amongst the Judge Magisters, Gabranth is known to be a brilliant solider13, and is respected by his fellow colleagues.

The career path of Gabranth is an unusual case -- Gabranth started out in the lowest social bracket of Archadia, but was able to enlist into the Order of Judges, eventually ascended through the ranks and became Judge Magister, due to having earned the favor of Emperor Gramis.14

As the person most trusted by Emperor Gramis, Gabranth was given the task to investigate and observe Vayne in secret by the Emperor. After the death of Emperor Gramis, Gabranth’s duties were significantly reduced.