For a list of the agents, see Category:Agent.
An agent is a type of operative.
It is certain field agents duties to remain unseen, and also unheard. These agents are also commonly referred to as spies. A lot of the time, these agents are sent into the field with only themselves or a second agent and are to carry out tasks that only someone who has gone unnoticed can accomplish. Whether it be to retrieve valuable information, rescue hostages, kidnap an individual or assassinate a threat to their agency/government, they are to do what it takes to leave no sign of them ever being in the area.
A number of times have been noted where these agents have been allowed to use what is known as Fifth Freedom, which means that they are allowed to do whatever is necessary to accomplish their task. While the use of non-lethal force is sometimes not an option, these agents are strongly recommended against it in their every day operations. The NSA has been known for using a number of these type of agents not only in the past, but in their current activities as well.
There are times when sending an agent in covertly wouldn't exactly get the job at hand finished. A lot of the time this is when an agent would be sent into a situation "undercover" to infiltrate an organization or group and become a member of the group. Sometimes their goal may be to gain the trust of members of the said group and build a reputation, alluding any suspicion that may come their way. Other times their goal may simply be to keep quite and just retrieve any information that may come their way, reporting it back to their headquarters in regular intervals. The CIA has been known for using these types of agents quite often.
"Double agent" is a term used to describe an agent that has been sent in by one organization to infiltrate another. These agents can originate from a government like facility, or a terroristic organization, both with the same goal; to perform tasks for the other group, build a trust between themselves and the leaders or members of the group and then find as much information on the opposing group or do what they can to stop actions that may harm the things or people that are in their groups best interest.
These agents are faced with hard decisions however, sometimes they may need to go against their morals or objectives and do things that they normally wouldn't do, such as killing or saving someone that they were advised not to do. These actions are choices that only someone in the position of the field operative can make, as everything they decide to do will affect how one organization views them. When referencing a double agent that had been sent into a terroristic organization to retrieve information, there may be a time when they will need to kill an innocent civilian in order to keep their cover. If the information they had been sent in to retrieve could save the lives of many others, the action may be just.
While these agents were sent in the field because they were highly trusted by their organization, there will always most likely be some level of suspicion from their original handlers. This is almost always out of fear that the agent had turned and began actually working for the other side. Every choice a double agent makes can make or brake their goals.
A field agent is any agent that is sent into a situation first hand. Not all agents wield weapons and infiltrate organizations, some agents' jobs are to go over the information that others collected, some work at the agency's headquarters (such as certain CIA agents). The field agent is sent in where they are needed and can have any number of tasks. They may need to remain covert, or go undercover. Almost always, field agents have a scheduled check in date and time with the headquarters of their organization, this is primarily for their safety. When working alone, or even in a small group, there is a chance that something could go wrong. Whether it be their cover being "blown" or just an accident, maintaining contact allows these agents to remain "safe" even when away from their homeland. If a scheduled check-in had been missed, this gives their agency a chance to send in other field agents to either attempt a evacuation or find information on their situation or whereabouts.