Answer:
The Secretary of State
Step-by-step explanation:
The Secretary of State is the head of the United States Department of State. This departments deals with foreign affairs and foreign policies and oversees the work of diplomats and ambassadors.
All embassies fall under the State Department's jurisdiction and all diplomats and ambassadors answer directly to the Secretary of State,.
Diplomats and ambassadors are appointed by the President and serve 'at his pleasure', meaning they can be dismissed at any time.