Secretary of Defense Gen. James Mattis let one journalist know how accurate his fearless reputation apparently is.

In a wide-ranging interview with CBS' John Dickerson, Mattis was asked, "What keeps you awake at night?"

Without a second to consider, Mattis responded: "Nothing. I keep other people awake at night."

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Mattis, a retired four-star Marine Corps general, is well-known as a tireless advocate for his men and his mission, and a tireless adversary of America's enemies.

Mattis earned the nickname "Mad Dog," though insists that was a name simply given to him by the press.

His fellow Marines instead reportedly nicknamed him the "Warrior Monk" for his lifestyle and continued study of war.

Several quotes befitting that reputation circled around during his nomination, often flippant and occasionally irreverent in nature.

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