Who is the Secretary of State?

The correct answer is Rex W. Tillerson, who served as the Secretary of State from February 2017 until March 2018 under President Donald Trump. The role of the Secretary of State is crucial as it involves overseeing the United States' foreign policy, representing the country to other nations, and managing diplomatic relations. Tillerson, who was previously the CEO of ExxonMobil, brought a business-oriented approach to the role.

The other individuals listed in the options held different significant positions within the U.S. government during that time. James Mattis was the Secretary of Defense, responsible for military operations and national defense. Mike Pence served as the Vice President, supporting the president and assuming duties in his absence. Robert Speer was the Acting Secretary of the Army, overseeing the Army's operations and policies. Their roles are distinct and separate from that of the Secretary of State, leading to the clear distinction that makes Tillerson the correct choice for this question.