Jim James MattisREUTERS/Mike SegarUS Secretary of Defense James Mattis walks past saluting cadets as he arrives for commencement ceremonies at West Point on May 27, 2017.

Defense Secretary James Mattis was legendary long before he agreed to join President Donald Trump's Cabinet.

The retired four-star general spent 44 years in the US Marine Corps, working his way up to Commander of US Central Command.

He's been called "Mad Dog" Mattis (a nickname he detests), "Warrior Monk" (because he's such an intellectual), and is beloved and respected by fellow Marines.

Mattis also has some of the best quotes of any general around. Here are 17 of his best.

This post is based on a previous story by Paul Szoldra.

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On meeting new people:

On meeting new people:

On collateral damage:

On collateral damage:

On taking a life:

On taking a life:

Warning US enemies:

Warning US enemies:

On foes opposing the US military:

On foes opposing the US military:

On failure:

On failure:

On the business of war:

On the business of war:

On defeating Al Qaeda:

On defeating Al Qaeda:

On the US Marines:

On the US Marines:

On using your head:

On using your head:

On presentations:

On presentations:

On leadership:

On leadership:

On fighting for democracy:

On fighting for democracy:

On treachery:

On treachery:

On thinking things through:

On thinking things through:

On what it means to be a US Marine:

On what it means to be a US Marine:

On combat:

On combat: