Each Preventer agent is assigned a codename based on one of the classical elements.
- Sally Po - Water
- Lucrezia Noin - Fire
- Lady Une - Gold (Endless Waltz novelization only)
- Zechs Merquise - Wind
- Chang Wufei
- Kathy Po
In A.C. 196, after the end of the Eve Wars and the founding of the Earth Sphere Unified Nation, the Preventer was created as an intelligence agency that answers directly to the ESUN President. The existence of the Preventer was highly classified, known only to the ESUN President and several key members of the government, since the existence of an armed peacekeeping force goes against the pacifist ideals of the ESUN.
The mission statement of the Preventer is the preservation of peace and prevention of conflicts in the Earth sphere. In order to accomplish this goal, the Preventer worked tirelessly to destroy excessive weapons (known as "kindling") and to stop large scale insurrections and terrorist activities (known as "fire disasters") before they start. Because of this, they are also referred to as the "Firefighters" (火消し).
The organization was headquartered in Brussels, the capital of the ESUN. In addition, it controlled a lunar base, where at least one cruiser was stationed.
Barton Foundation Investigation
On the colonies, there were the movements of the Barton Foundation, the original architects of Operation Meteor. This didn't go unnoticed by the Preventer or the Gundam Pilots. Heero and Duo planned on infiltrating Colony L3 X-18999 to rescue kidnapped Vice Minister Relena Darlian. Sally and Lucrezia assisted them by destroying the mobile suits guarding the entrances.
Mariemaia Earth Invasion
The Mariemaia Army was poised to invade Earth, due to the dissolution of its armed forces. However, as the first wave of transports deployed, the Tallgeese III, piloted by Zechs Marquise, destroyed all of them. Unfortunately, as he was poised to destroy the MA base, Dekim Barton threatened to drop colony L3 X-18999 onto Earth, thus completing the original Operation Meteor. Zechs had no choice but to let the other transports go past.
Luckily, the Gundam Pilots stabilized X-18999 and prevented it from dropping, allowing Zechs to destroy Dekim's base. However, Dekim managed to escape.
The ESUN capital of Belgium was invaded by the Mariemaia Army, taking control of the Earth Sphere. Lady Une infiltrated the presidential bunker from a secret passage while the Tallgeese III and a Taurus acted as distractions. Both Mobile Suits fought against more than four hundred Mariemaia Army Mobile Suits, and managed to disable many of them without killing any pilots. Soon, three Gundams arrived to help, but they, along with the Preventer mobile suits, soon ran out of energy and ammunition due to the sheer number of enemies. However, a heavily damaged Wing Zero suddenly appears in the sky and attempts to destroy the presidential bunker. Just as the shelter was about to collapse, Une saves Relena and Mariemaia from being crushed by falling debris. Soon, the populace decided to stand up against the Bartons and Dekim was killed by one of his own men, and true peace reigned over the Earth.
In the year Mars Century (M.C.) 0022, Preventer agent Kathy Po, daughter of missing agent Sally Po, is given orders by ESUN President Dorothy Catalonia to launch a mission known as Operation Mythos. She meets her superior officer Master Chang at the Mars Preventer Base to deliver vital data and information of the orders received. There, she meets the awakened pilot Heero Yuy, who joins the Preventer along with a mysterious priest named Father Maxwell and his son Duo for the mission.
- OZ-00MS2B Tallgeese III
- OZ-12SMS Taurus
- OZ-06MS Leo
- Snow White
- Preventer Cruiser
- Preventer Shuttle
- In Super Robot Wars Alpha Gaiden, former members of Londo Bell assume this name for their forces, not only because of the Endless Waltz plot, which they must stop in the early arc of the game, but also because they are trying to prevent a disaster that could befall Earth and the colonies from the previous game.
- The Preventers and Londo Bell are very similar, as both were a new peacekeeping force that replaced the previously corrupt one (the Preventers replacing OZ; Londo Bell replacing the Titans).