The Agents are things that serve the will of the Titans, or the things in the cracks of the Titans' prisons. They blend themselves with a mortal person and change it with supernatural traits. Given time they will merge completely with someone and destroy that person's soul. They usually travel in packs of three, using threats, violence, and murder to fulfill their shady unknown missions.
No matter the time, place, or weather, they usually dress in similar manners, using some kind of dark suit, or jacket, black sunglasses, and sometimes a hat. They can pass as normal humans by copying their behaviors and backgrounds, but their eyes will always have an unnatural aspect in them. They all can have different traits, but they will always have some kind of terrifying presence or gaze if people look into their eyes.
They somehow seem to be able to communicate with others over long distances, and if one of them dies, it will return to whatever place it is needed and give information to its master. They never truly die, only the body that contains them. It gets tricky because if the dominated person lives too much time with the Agent, the person will no longer exists, but the person can be separated from it with the proper procedures.
There are some ways to deal with Agents. There are magical rituals to exorcise them from a person and imprison or destroy them. Imprison it is safer and can be done within a few hours, although destroying an Agent can be much more complicated and not certain. This is one of the reasons that destroying them is not an easy task. The only problem with imprisoning an Agent is that the object in question still can "bleed" the Agent's will and influence the person who possess that object.