Members of the president's Cabinet, often just called the Cabinet, are official advisers to the president who often play a role in various parts of the Executive Branch. The president selects members of the Cabinet, but each member has to be approved by the Senate.
While the U.S. Constitution makes the Cabinet an official governmental entity, it doesn't state what departments must be part of it. The original departments of the Cabinet included a Secretary of State, a Secretary of the Treasury, a Secretary of War and an Attorney General. These positions still exist, but the Secretary of War is now called the Secretary of Defense, since the Department of War became the Department of Defense in 1947. Other fields have since become parts of the Cabinet, with positions reserved for transportation, labor, education and commerce.
While presidents can defer power to the members of the Cabinet, they are under no obligation to follow the advice the Cabinet gives. Some presidents give the Cabinet relatively little power and work with other members of the executive branch. Presidents may defer certain roles to the vice president, the chief of staff or appointed representatives. However, Cabinet-level officers have positions in the line of succession; the Secretary of State, for example, is fourth in line to become president.