President-elect Donald Trump has chosen retired Marine Gen. James N. Mattis to be secretary of defense, nominating a former senior military officer who led operations across the Middle East to run the Pentagon less than four years after he hung up his uniform, according to people familiar with the decision.

To take the job, Mattis will need Congress to pass new legislation to bypass a federal law that states secretaries of defense must not have been on active duty in the previous seven years. Congress has granted a similar exception just once, when Gen. George C. Marshall was appointed to the job in 1950.

An announcement is likely by early next week, according to the people familiar with the decision.

Mattis, 66, retired as the chief of U.S. Central Command in spring 2013 after serving more than four decades in the Marine Corps. He is known as one of the most influential military leaders of his generation, serving as a strategic thinker while occasionally drawing rebukes for his aggressive talk. Since retiring, he has served as a consultant and as a visiting fellow with the Hoover Institution, a think tank at Stanford University.

Like Trump, Mattis favors a tougher stance against U.S. adversaries abroad, especially Iran. The general, speaking at the Center for Strategic and International Studies in April, said that while security discussions often focus on terrorist groups like the Islamic State or al-Qaida, the Iranian regime is “the single most enduring threat to stability and peace in the Middle East.”

Mattis said the next president “is going to inherit a mess,” and argued that the nuclear deal signed by the Obama administration last year may slow Iran’s ambitions to get a nuclear weapon, but won’t stop them.

“In terms of strengthening America’s global standing among European and Mid-Eastern nations alike, the sense is that the America has become somewhat irrelevant in the Middle East, and we certainly have the least influence in 40 years,” Mattis said.

But Mattis may break with Trump’s practice of calling out allies for not doing enough to build stability. In the same event, Mattis said he was troubled by President Obama’s remarks in a March interview with The Atlantic that there were “free riders” accepting U.S. help without reciprocating. He added that he read the Atlantic story after printing it out, and briefly thought he had accidentally mixed it with a news clip that highlighted Trump’s views.

“The President-elect is smart to think about putting someone as respected as Jim Mattis in this role,” said a former senior Pentagon official. “He’s a warrior, scholar, and straight shooter – literally and figuratively. He speaks truth to everyone, and would certainly speak truth to this new commander-in-chief.”

But the official, who spoke on condition of anonymity to discuss Trump’s personnel choices, said, “If there’s any concern at all, it’s the principle of civilian control over the military. This role was never intended to be a kind of Joint Chiefs of Staff on steroids, and that’s the biggest single risk tied to Mattis. For Mattis, the biggest risk for him personally is that he’ll have a national security adviser in the form of Mike Flynn whose management style and extreme views may arch Mattis’ eyebrows and cause conflict over time. It’s no fun to be secretary of defense if you have to constantly feud with the White House.”

Mattis served from November 2007 to August 2010 as the supreme allied commander of transformation for the North Atlantic Treaty Organization, in which he focused on improving the military effectiveness of allies. Trump called NATO “obsolete” earlier this year, before saying later that he was “all for NATO,” but wanted all members to spend at least 2 percent of their gross domestic product on defense, a NATO goal.

Mattis will join the Trump administration after calls by some conservatives for him to join the presidential race in a longshot independent bid aimed at derailing Trump’s ascent this spring. The general declined to do so, saying he didn’t understand the speculation.

Mattis, whose nicknames include “Mad Dog” and the “Warrior Monk,” has had a leading hand in some of the U.S. military’s most significant operations in the last 20 years. As a one-star general, he led an amphibious task force of Marines that carried out a November 2001 raid in helicopters on Afghanistan’s Kandahar province, giving the Pentagon a new foothold against the Taliban after the Sept. 11, 2001, attacks. Using the call sign “Chaos,” he commanded a division of Marines during the U.S. invasion of Iraq in 2003, and returned there the following year to lead Marines in bloody street fighting in the city of Fallujah.

Mattis continued to rise through the ranks and establish his credentials as a military thinker, co-authoring the U.S. military’s new counterinsurgency manual with then-Army Lt. Gen. David Petraeus while Mattis was a three-star general at Quantico, Va.

He was considered a leading contender to become commandant of the Marine Corps in 2010, but was bypassed in favor of Gen. James F. Amos. Instead, Mattis replaced Petraeus as the chief of Central Command, overseeing U.S. military operations across the Middle East.

Even though Central Command didn’t encompass Israel, Gen. Mattis made a concerted effort to reach out to his Israeli military counterparts, according to Steven Simon, who worked with Gen. Mattis when he served on Obama’s National Security Council.

Simon, who now teaches at Amherst College, said Mattis made frequent stops in Israel during trips to the region, part of an effort to encourage the Jewish State and its Arab neighbors to work together to counter Iranian influence. “They respected Mattis because they saw him as a straight shooter and a good listener,” said Simon of the Israelis and Arabs.

The general retired from that position about five months earlier than expected in 2013, prompting speculation that he was forced out after clashing with some in the Obama administration on Iran policy. U.S. officials denied that was the case at the time, and Mattis declined to comment.

Mattis occasionally has come under scrutiny for impolitic remarks. Most notably, he said in 2005 during a panel discussion in San Diego that “it’s fun to shoot some people” and “I like brawling,” drawing criticism from then-Marine Commandant Gen. Michael Hagee. But Hagee also later backed Mattis, saying the general often spoke with candor to reflect the horrors of war. Other supporters noted that he often stressed to his own troops that it was important to treat civilians in a combat zone with care.

It’s unclear whether the legislation required to make Mattis Pentagon chief will be difficult to obtain from Congress. The 1947 national security law said that any general must wait 10 years from leaving active duty before becoming defense secretary. An exception was granted on a one-time basis for Marshall, with lawmakers saying in special legislation at the time that it is “sense of the Congress that after General Marshall leaves the office of Secretary of Defense, no additional appointments of military men to that office shall be approved.”

The 10-year period was reduced to seven years in 2008 for several senior civilian defense positions, including defense secretary.

The Washington Post’s Philip Rucker, Adam Entous and Missy Ryan contributed to this report.