President-elect Donald Trump’s nominee for secretary of defense, retired four-star Marine Gen. James Mattis, is worried that the U.S. is retreating in a chaotic world.

“Right now we have an America that is starting to reduce its role in the world,” Mattis said in a speech at The Heritage Foundation last year. “That’s not good.”

Mattis, known and admired as “Mad Dog” in the military, is sober about what impact America can ultimately have on world events. But that doesn’t mean the U.S. shouldn’t try to exert its influence, he says.

“I have never thought it necessary to patronize the American people,” Mattis, 66, said in the same speech. “You are not going to get it completely right. You just don’t want to get it completely wrong.”

Mattis has lived this reality.

During a 41-year military career, he most recently ran the United States Central Command, which oversees military operations in the Middle East and Southwest Asia, from 2010 to 2013.

Before that, he was most known for his leadership in Iraq and Afghanistan.

“We are going to appoint ‘Mad Dog’ Mattis as our secretary of defense,” Trump told supporters at a rally on Thursday night in Cincinnati, Ohio. “But we’re not announcing it until Monday, so don’t tell anybody. Mad Dog. He’s great. He is great.”

Mattis led the 1st Marine Division during the 2003 invasion of Iraq to defeat Saddam Hussein. He later led the Marines in the bloodiest battle of the Iraq War to retake the city of Fallujah from Sunni insurgents in 2004.

Today, the U.S. remains engaged in war in Iraq as it leads a coalition to dislodge the Islamic State, or ISIS, from the country.

As Trump taps Mattis to lead the Pentagon in its defense of the U.S., here are four things to consider about the outspoken, well-read Marine general, also known as “Warrior Monk.”

1. Critical of Obama Middle East Strategy

Since Mattis left the Central Command, reportedly because the Obama administration believed he was too hawkish on Iran, he’s been a frequent critic of Washington’s Middle East policies.

“Whether it is right or not, the perception [among allies in the Middle East] is we are pulling back, and going into that vacuum are rather unsavory impulses,” Mattis said in the Heritage speech.

Mattis has said that responding to “political Islam” is a major security issue facing the U.S., one that underlies the various conflicts in the Middle East. It’s a place that “still has me going through therapy,” he has joked.

“Is political Islam in the best interest of the United States?” Mattis said. “I suggest the answer is no, but we need to have the discussion. If we won’t even ask the question, how do we even recognize which is our side in a fight?”

He also has said that Iran is a greater threat than terrorist groups such as ISIS or al-Qaeda.

Speaking at the Center for Strategic and International Studies in April, Mattis said Iran is “the single most enduring threat to stability and peace in the Middle East.”

But in the same speech, Mattis did not advocate canceling the nuclear deal the Obama administration and other foreign powers negotiated with Iran.

He said the nuclear deal may slow Iran’s pathway to a nuclear weapon, and not stop the regime.

Yet “absent a clear and present violation,” he did not know how the U.S. could back away from the deal, because unilateral action against Iran would not be successful unless allies party to the agreement also participate.

“What we achieved was a nuclear pause, not a nuclear halt,” Mattis said. “We’re going to have to plan for the worst.”

2. ‘Serious’ Russia Threat

Mattis may diverge with Trump on Russia policy.

In the Heritage speech, Mattis said the Russia “situation” is “much more severe and much more serious than we have acknowledged.”

“Putin goes to bed at night knowing he can break all the rules, and the West will follow all the rules,” Mattis said. “That is a very dangerous dichotomy in the way the world is being run.”

Russian President Vladimir Putin is militarily supporting the brutal regime of President Bashar al-Assad in Syria. Trump has suggested he could work with Russia to defeat ISIS.

Meanwhile, Russia is engaged in Europe’s only active war. Pro-Russian rebels have seized territory in eastern Ukraine, and Russia annexed Crimea in 2014.

In the Heritage speech, Mattis warned that Russia “is out to break NATO [the North Atlantic Treaty Organization] apart.”

Early in his campaign, Trump called NATO “obsolete” before saying later that he was “all for NATO.”

Mattis said the U.S. must respond to Russia’s aggressiveness.

“No dialogue with Putin is very dangerous,” Mattis said.

3. Colorful Speaking Style

A voracious reader who has never owned a television or been married, Mattis is known for using colorful language to describe life in the military.

For example, during a panel discussion in 2005, he described how enjoyable it can be to kill the enemy in war.

“Actually, it’s quite fun to fight them, you know. It’s a hell of a hoot,” Mattis said, “It’s fun to shoot some people. I’ll be right up there with you. I like brawling.”

The San Diego Union-Tribune compiled more of Mattis’ interesting quotes over the years:

“I come in peace. I didn’t bring artillery. But I’m pleading with you, with tears in my eyes: If you [expletive] with me, I’ll kill you all.”

“The most important 6 inches on the battlefield is between your ears.”

“There is nothing better than getting shot at and missed. It’s really great.”

“I’m going to plead with you, do not cross us. Because if you do, the survivors will write about what we do here for 10,000 years.”

4. Confirmation Consideration

Mattis will need supermajority support in the Senate—60 votes—to be confirmed as defense secretary. That means Mattis is the only Trump Cabinet pick so far who Democrats can unilaterally block.

This unique condition is due to Mattis’ recent retirement from the military.

Under federal law, defense secretaries must have been out of service for seven years. So for Mattis to be confirmed, Congress must pass legislation granting him a waiver to serve in the Cabinet since he left the military four years ago.

Sen. Kirsten Gillibrand, D-N.Y., said she will oppose a waiver for Mattis because “civilian control of our military is a fundamental principle of American democracy, and I will not vote for an exception to this rule.”

Republicans are expected to control 52 Senate seats next year, meaning Mattis would need votes from at least eight Democrats.

Congress has granted a similar exemption just once, when George Marshall was appointed to the job in 1950. Marshall was the last ranking general to be defense secretary.