Retired U.S. Marine Corps General James Mattis is President Trump's Secretary of Defense. Here's what you need to know about "Mad Dog Mattis." (Jenny Starrs/The Washington Post)

Donald Trump has professed that he's not much of a reader. He told The Washington Post over the summer that he had not read biographies of presidents because he does not have the time and that he makes the right decisions "with very little knowledge other than the knowledge I [already] had, plus the words ‘common sense,’ because I have a lot of common sense and I have a lot of business ability." When Fox News host Megyn Kelly interviewed Trump in her prime-time special in May, she asked him about the last book he'd read. "I read passages, I read … 'areas,' I'll read chapters," he said. "I just, I don't have the time."

Perhaps a man he has reportedly selected as his Secretary of Defense will rub off on him. Retired Marine Gen. James Mattis, nicknamed "Mad Dog," is known for his gruff and blunt quotes. ("Be polite. Be professional. But have a plan to kill everybody you meet.") He's been hailed for his battlefield successes, his strategic mind and his bond with rank-and-file soldiers. He's been called a "warrior monk" and has a disdain for PowerPoint.

But Mattis -- who, notably, would need a legislative waiver to be confirmed since he only retired in 2013 -- is also frequently noted for being an avid reader steeped in history. Michèle Flournoy, the former undersecretary of defense who was widely thought to be a likely front-runner for the same job had Clinton won the election, told NPR Mattis "would be an outstanding candidate," calling him a "student of history." Sen. John McCain, in a statement endorsing Mattis on Monday, called him a "forthright strategic thinker."

New America senior adviser and former Washington Post military correspondent Thomas Ricks wrote in Foreign Policy last month that Mattis pushes "himself and others to stretch their minds," pointing out how his reading habits set him apart from Trump. "He prepared a reading list for his officers before deploying to Iraq in 2004 and required that it be studied," Ricks wrote. "Start reading the works of Sir Hew Strachan, Mattis’ favorite strategist."

In a blog post from 2013, the year Mattis retired, military historian Jill Russell shared a 2003 email, with his permission, that Mattis had written and which had been widely circulated within the Marine Corps. A colleague had asked why it is important for officers to take time to read and study.

Mattis wrote that "the problem with being too busy to read is that you learn by experience (or by your men's experience), i.e. the hard way. By reading, you learn through others' experiences, generally a better way to do business, especially in our line of work where the consequences of incompetence are so final for young men." His reading, he wrote, provides guidance and perspective. "It doesn't give me all the answers, but it lights what is often a dark path ahead."

He ran through a litany of books about history and military history that had guided him -- from T.E. Lawrence's "Seven Pillars of Wisdom" to Liddell Hart's biography of Civil War Gen. Sherman to Bruce Catton's "Grant Takes Command," noting its lesson on the "need for commanders to get along," with " 'commanders’ relationships' being more important than 'command relationships.' "

"Ultimately, a real understanding of history means that we face NOTHING new under the sun," he wrote. "I believe that many of my young guys lived because I didn’t waste their lives because I didn’t have the vision in my mind of how to destroy the enemy at least cost to our guys and to the innocents on the battlefields."

More recently, in mid-October, Mattis hailed the importance of reading twice in a video posted by the Marines about leadership lessons from his career. Asked by one Marine about what books he recommends, he pointed to a required reading list, saying that such books should help young officers realize "you as a young leader will never face anything worse than what fighters have faced in the past." He called out Eugene Sledge's book "With the Old Breed: At Peleliu and Okinawa," ("you'll find the spirit of the Marine Corps overcoming the most difficult combat conditions," he said), noting the list "requires you to do a lot of reading because there are many different styles of leadership. You must stay authentic to who you are but at the same time we expect you to lead in no uncertain terms."

Another Marine asked how he keeps developing as a leader. Mattis said: "You stay teachable most by reading books. By reading what other people went through. I can't tell you the number of times I looked down at what was going on on the ground or I was engaged in a fight somewhere and I knew within a couple of minutes how I was going to screw up the enemy. And I knew it because I'd done so much reading. I knew what I was going to do because I'd seen other similar situations in the reading. I knew how they'd been dealt with successfully or unsuccessfully."

Read also:

Donald Trump's binder full of white men

What a professor who studies outside leaders has to say about Donald Trump

Like On Leadership? Follow us on Facebook and Twitter, and subscribe to our podcast on iTunes.