General Mattis became the source of words to live by in the military.

Here's some of his most notable phrases:

"Be polite, be professional, but have a plan to kill everybody you meet."

"The most important six inches on the battlefield is between your ears."

"Don't create more enemies than you take out by some immoral act."

"You cannot allow any of your people to avoid the brutal facts. If they start living in a dream world, it's going to be bad."

And a rather odd one: "Powerpoint makes us stupid."