President-elect Donald Trump Thursday selected retired Marine Gen. James N. Mattis to be the next defense secretary.

Mattis, 66, nicknamed “Mad Dog” and “Warrior Monk,” headed the U.S. Central Command for three years before retiring as a four-star general in 2013 after 44 years in the Marine Corps. He retired after clashing with the Obama administration over outreach to Iran, which he called unwise.

Earlier this year, anti-Trump Republicans tried to get Mattis to run for president as a third-party candidate.

Trump made the announcement during his rally in Ohio but had telegraphed his decision last week in a meeting with New York Times editors and reporters.

“I think it’s time maybe, it’s time for a general [at the Pentagon],” said Trump, who was critical of the military during his campaign, claiming to know more about the Islamic State group than the generals. “Look what’s going on. We don’t win, we can’t beat anybody.”

The Los Angeles Times said Mattis is known as a hard-charging but scholarly leader who is as likely to quote from Shakespeare or Greek poets as military strategists in speeches.

“He is the combination of strategic thinker and successful operator at all levels of warfare,” retired Marine Maj. Gen. Arnold Punaro, author of “On War and Politics: The Battlefield Inside Washington's Beltway,” told the Times. “His entire life has been learning about and implementing a strong national defense.”

Before Mattis could be confirmed as head of the Pentagon, Congress would have to grant a waiver because he has not been out of the military for seven years, a requirement meant to keep the government out of the hands of the military’s control. The only other time such a waiver was granted was 1950 when President Harry Truman nominated Gen. George Marshall, who already had served as secretary of state.

Sen. John McCain, R-Ariz., who heads the committee that will hold confirmation hearings on the defense chief, described Mattis as “one of the finest military officers of his generation.”

Mattis’ view on Iran appears to coincide with Trump’s, and he appears to have changed Trump’s mind on the effectiveness of waterboarding. Trump said he was impressed with Mattis opinion that a “pack of cigarettes and a couple of beers” are more effective at eliciting useful information.

Trump already has nominated retired Army Lt. Gen. Michael Flynn as his national security adviser and has interviewed retired Army Gen. David Petraeus, who headed the CIA until he was forced to resign for turning over classified material to a biographer with whom he was having an affair, for secretary of state.

“Most of these officers are relatively non-partisan, publicly endorsed no candidate during the campaign, and have lifelong records of public service leading large, complex organizations,” Dave Barno, a retired Army general, told Time magazine. “They could bring a wealth of sober judgment and experience to a Trump foreign policy team in need of both.”