When it comes to Donald Rumsfeld, he would be considered a bureaucrat since he was appointed to be Secretary of Defense. All bureaucrats working for the government are agents in some way. The Department of Defense and federal level bureaucracies can sometimes controlled by the executive branch, the president can even nominate who they choose to be secretary of defense. Usually, congress is the one that controls most agencies.
Besides making the government
run more efficiently, the bureaucrats also implement laws that congress writes. They can enforce laws and even make them which can lead them to over step their boundaries with the legislation branch. For example, if you violate any FCC regulations, they can fine you like any local police.
One reason that bureaucracies have grown is that more issues concerning the stability of the environment have strung up. Also, it has to be noted that when congress does make a bureaucracy it usually stays permanent or stays for many years. They have also grown simply because congress keeps making them and delegating powers, this is because they fill roles that the private sector might not fill such as meat inspection.