In the film The Matrix agents are computer programs that resemble humans charged with hunting down anyone who poses a threat to the Matrix including rebels and those affiliated with them as well as renegade programs.
Agents masquerade as government agents resembling the Men In Black of UFO conspiracy theories, always dressing in dark suits and sunglasses and wearing earpieces that can be used not only to communicate with each other but to tap into the matrix and locate abnormalities. With the exception of Agent Smith, Agents seem to lack personality as they talk in monotone voices and never express any form of emotion.
Agents have superhuman abilities. They are capable of dodging bullets, punching through stone and taking over the body of anyone who's mind is imprisoned in the matrix. They are also seeming unable to feel pain. They also have pinpoint accuracy and always carry concealed desert eagles.
Agents can never truly die as when the are killed they are sent back to the Machine mainframe leaving the body they were inhabiting and can respawn using their earlier mentioned ability to take over one's body. The only way an agent can truly die is if they are deleted by the Machines or some other entity.
The Machines have influenced the government into doing the Agents' bidding as the agents operate under the guise of investigating computer crime and terrorism and are able issue orders to the police department.
The agents from the first Matrix film were deleted and replaced with upgraded agents who were larger, stronger, and faster and appeared in the second Matrix film. Some agents are granted authority over others, such as Agent Smith who commanded two other agents before betraying the Machines after his programming was disrupted, or Agent Johnson who led three upgraded agents in The Matrix Reloaded.
Neo is the only person to ever defeat an agent without the help of the environment. To date, Agents are still active in the Matrix universe.
Those are Agents holding him, three of them.