in a republican state the head of the state is
Head of state An independent nation state normally has a head of state, and determines the extent of its head's executive powers of government or formal representational functions.[8] In protocolary terms, the head of a sovereign, independent state is usually identified as the person who, according to that state's constitution, is the reigning monarch, in the case of a monarchy, or the president, in the case of a republic.
United States Department of State The Department is led by the Secretary of State, who is nominated by the President and confirmed by the Senate and is a member of the Cabinet. The current Secretary of State is Rex Tillerson, beginning 1 February 2017. The Secretary of State is the first Cabinet official in the order of precedence and in the presidential line of succession, after the President pro tempore of the Senate.