Which individual is the Secretary of Defense?

The Secretary of Defense is a key leader within the U.S. government, responsible for overseeing the Department of Defense and coordinating military policies and operations. The correct individual in this context is the Honorable Mr. Mattis, who served as Secretary of Defense from January 20, 2017, to January 1, 2019, under President Trump.

His extensive military background as a retired Marine Corps General and his experience in various leadership roles provided him with a strong foundation for this position. Mattis was known for his strategic approach to national defense and his ability to engage with military and civilian leadership wisely.

The other individuals mentioned do not currently hold the position or did not serve in it during the relevant timeframe. Spencer was the Secretary of the Navy; the former president, Trump, was not a Secretary of Defense, and Smith has not held the position of Secretary of Defense as of October 2023. Understanding the historical context and the timeline of these appointments is crucial for recognizing the correct answer.