Who is Defense Secretary James Mattis? 6 things to know

“Because you have the right to have a Secretary of Defense whose views are better aligned with yours on these and other subjects, I believe it is right for me to step down from my position," he wrote.

Here are six things to know about Mattis.

1 - Mattis became the 26th U.S. secretary of defense for the Trump administration on Jan. 20, 2017, after retiring from the Marine Corps in 2013.

2 - Mattis spent four decades in uniform, commanding "the Marines at all levels, from infantry rifle platoon to a Marine Expeditionary Force," according to his biography.

3 - After the 9/11 terrorist attack, Mattis led an expeditionary brigade in Afghanistan, and during the 2003 invasion of Iraq, he commanded the 1st Marine Division. He also served as the 11th commander of the U.S. Central Command during the Obama administration.

4 - James Norman Mattis, 68, was born on Sept. 8, 1950, and is a native of Richland, Washington. He graduated from Central Washington University in 1971. He is also a graduate of the U.S. Marine Corps Amphibious Warfare School, U.S. Marine Corps Command and Staff College and the National War College.

5 - According to his biography, Mattis is known for his interest in military history and world history, and once had a personal library with thousands of books. He also reportedly liked to hand out required reading lists to Marines under his command and required them to learn about the regions in the world before they deployed to those areas.

6 – Mattis, a lifelong bachelor, had several nicknames over his long military career, including "Warrior Monk" and "Mad Dog Mattis." He reportedly did not like the nickname "Mad Dog," which his troops gave him during the Iraq War.

Credit: The Associated Press

Credit: The Associated Press