United States Secretary of State
The Secretary of State is the head of the United States Department of State, concerned with foreign affairs. He or she is a member of the President's Cabinet. As the highest ranking cabinet member, the Secretary of State is fourth in line to succeed the Presidency, after the Vice President, Speaker of the House, and President pro tempore of the Senate.
If the Secretary resigns, he is replaced by the Deputy Secretary who then becomes acting Secretary of State until the President and Congress approve a formal replacement.