By Idrees Ali and Phil Stewart

WASHINGTON (Reuters) - Dan Caine may not have been on Washington's radar before Friday night. But President Donald Trump's fascination with the retired three-star general, his surprise pick to become the next chairman of the Joint Chiefs of Staff, appears to go back to their first meeting in Iraq in 2018.

Caine, then the deputy commander of a special operations task force fighting Islamic State, told the president that the militant group could be destroyed in just a week, Trump recalled during a speech to the Conservative Political Action (WA: ACT ) Conference in 2019.

Since then, he has retold the story about how he met "Razin" Caine multiple times - and the praise has only grown more effusive.

"He's a real general, not a television general," Trump said in Miami on Wednesday, two days before his Truth Social post catapulted Caine from retirement to a nomination to be the most senior active-duty officer in the U.S. military.

If approved by the Senate, Caine will take over a military that is reeling from change in the first 30 days of the Trump administration and will inherit a Joint Staff rattled by Trump's surprise firing of the chairman of the Joint Chiefs of Staff, Air Force General C.Q. Brown.

Caine, a retired F-16 pilot, will be promoted to four-star general, and then have to undergo a potentially grueling Senate confirmation process to get a four-year term as the uniformed head of the nation's military.

UNCONVENTIONAL PICK

Caine's military career is a far cry from the traditional path to becoming the president's top military adviser. Previous generals and admirals have led a combatant command or a military branch of service.

Caine did not rise that high in the ranks before retirement. According to Trump, he was "passed over for promotion by Sleepy Joe Biden," whom Trump defeated in November's presidential campaign.

"But not anymore!", Trump wrote on Truth Social.

Earlier this year Caine described on a podcast how as a young man he wanted to follow in the footsteps of his father, a fighter pilot.

"We started moving around as a kid. So I felt like this was something that I really, really, really wanted to do, was fly jets in the Air Force," Caine said.

He graduated in 1990 from the Virginia Military Institute with a bachelor's degree in Arts and Economics.

Caine, who flew more than 2,800 hours in the F-16, was one of the pilots tasked with protecting Washington on September 11, 2001, when al Qaeda hijackers slammed commercial jets into the Pentagon and the World Trade Center in New York City.

Caine realized he might have to shoot down a hijacked plane if one crossed his path.

"I was very mindful that if we made a mistake or if we got it wrong or if we missed somebody and we did not shoot, the consequences of that could be catastrophic," Caine, who has also flown the T-37 and T-38 aircraft, said in an article posted on the CIA website.

Caine held a number of posts in the capital from 2005. He was as a special assistant to the secretary at the Department of Agriculture and then policy director for counterterrorism at the White House's homeland security council.

According to his official Air Force biography, Caine was a part-time member of the National Guard and "a serial entrepreneur and investor" from 2009 to 2016.

He was most recently the associate director for military affairs at the Central Intelligence Agency, before his retirement late last year.

But it was his time in Iraq from 2018 to 2019 that helped him gain Trump's attention.

Caine will be under particular scrutiny to ensure that he is apolitical, a concern that was heightened by the Friday night firing of Brown, a four-star general. Uniformed military officials are supposed to be loyal to the U.S. Constitution and independent of any party or political movement.

A senior U.S. military official who has worked with Caine for more than a decade said he would seek to keep the military out of politics.

Caine "puts the mission and troops above politics. He is not a political guy," the official said.

How far Cain can keep the military out of politics may largely depend on Trump - who in the past has dragged the military into partisan issues.

In a recent re-telling of their first meeting in Iraq, Trump said that Caine was in the hangar where service members started putting on "Make America Great Again" hats.

"They all put on the Make America Great Again hat. Not supposed to do it," Trump said during a speech last year.

"I said, 'you're not supposed to do that. You know that.' They said, 'It's OK, sir. We don't care.'"