Donald Trump's pick for defence secretary is a hard-charging former marine general nicknamed Mad Dog who, despite his rank, regularly rode convoys into combat during the Iraq invasion. 
James Mattis, former commander of U.S. Central Command, also has a gift for boot-stomping aphorisms.
"Be polite, be professional, but have a plan to kill everybody you meet," Mattis reportedly told marines stationed in Iraq.
But don't be misled by the colourful myth-making, says former U.S. Army general Barry McCaffrey. Mattis reportedly did not care for the Mad Dog label, a moniker that McCaffrey says belies a careful and studied military mind.
"The least of our worries ought to be that Mattis is a 'Mad Dog,'" says the Seattle-based four-star officer, who applauds Mattis's nomination as a buffer against what he calls an "ignorant and erratic" Trump brain trust. 
As much as the appointment should "scare the daylights" out of enemies of the U.S., McCaffrey says, expect the 66-year-old to be a "moderating voice" in the West Wing if he's confirmed.
"We'll have a steady, knowledgeable hand at defence to counter the president-elect's lack of experience and impulsiveness."
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U.S. soldiers take part in a live shooting exercise during U.S. operation "Atlantic Resolve" in Adazi, Latvia, earlier this year. If confirmed, Mattis would have the authority to send troops into battle. (Ints Kalnins/Reuters)
Tapping the 41-year Marine Corps veteran brings serious heft to security matters, military scholars say — particularly with regard to Mideast affairs, U.S.-Russia relations, recognizing the value of NATO and rethinking Trump's pledge to "rip up" the Iran nuclear deal.
To McCaffrey, Trump's pick is a "warrior-monk intellectual" with astute knowledge of military history and tactics that will be invaluable in the new administration.
"If I was a jihadist, I'd be digging a tunnel down into the basement and be 60 days into it when they take office."

Could sway Trump against torture

Perhaps more importantly, Mattis seems to wield influence on the soon-to-be Commander-in-Chief, notes Charles Dunlap, a retired U.S. Air Force major-general who knows Mattis personally.
"One example is how, after one relatively short meeting, he had Trump rethinking his controversial views on torture," says Dunlap, a Duke University law professor.
The defence nominee's conversation in Trump Tower last month "surprised" Trump, who told reporters that Mattis's objection to waterboarding gave him pause.
That's noteworthy because they diverge on other issues in which Mattis might hold sway.