Editor’s note: This article by Richard Sisk originally appeared on Military.com, a leading source of news for the military and veteran community.

President-elect Joe Biden's choice of retired Gen. Lloyd Austin, former commander of U.S. Central Command, rocked a defense community certain the job would go to former Pentagon official Michele Flournoy and wary of installing another recently retired general as the Defense Department's top civilian leader.

A noted introvert who avoided most interviews, Austin's most public moment came perhaps in September 2015, when he found himself on the receiving end of a tongue-lashing from Sen. John McCain, then the chairman of the Senate Armed Services Committee, over conflicting testimony about counter-ISIS efforts in Iraq and Syria.

Those who worked with him at different points during his 41-year Army career paint a complex picture of a well credentialed officer who cut an impressive figure -- opting, for example, to carry a loaded M4 carbine as his sidearm in Iraq instead of a pistol like most generals, to the delight of his troops. But, some said, he at times fell short when it came to big-picture strategic thinking and pushing back when needed on executive-level policy in light of conditions on the ground.

Retired Army Maj. Gen. Paul Eaton, who served with Austin when they were both lieutenant colonels in the 10th Mountain Division, called Austin "a man of the highest integrity. Steady in the saddle. Great command climate. General Austin is a great pick to lead our military in a dangerous world."

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The choice of Austin, who would become the first Black secretary of defense, would also send a strong message within the ranks and to the world of the new administration's commitment to diversity, Eaton said in a statement.

"Aside from his credentials, this historic pick sends a sorely needed message to our men and women in uniform -- that someone who looks like so many of them is finally leading the Pentagon," said Eaton, a senior adviser to the VoteVets organization.

Alex Plitsas, a former enlisted Army reservist who served under Austin in Iraq, called him a "good man," but said he found himself critical, at times, of his leadership.

Plitsas served as a planner in the Special Programs shop in 2010, while Austin was commander of U.S. Forces-Iraq, overseeing a drawdown of combat efforts. Plitsas said staff were concerned that a new enemy would arise as U.S. troops pulled out of the country, and worried that Austin wasn't presenting these concerns to a White House eager to leave the war behind.

"I didn't get the same feeling from him nor amongst the other staff members that he was a true strategic thinker," Plitsas said. "All of the questions we were asked by him and things we were asked to do, they were all tactically focused; it wasn't focused on an overarching strategy which is what you would expect from a commanding general."

This was the same time, Plitsas noted, that Austin developed a professional rapport with Biden, then vice president, who managed the Iraq portfolio. They'd spend more time together at the White House after Austin took command of CENTCOM in 2013.

In an essay published in The Atlantic Tuesday afternoon, Biden himself described his relationship with Austin and why he chose him, calling him a "true and tested soldier."

Then-Vice President Joe Biden speaks to the audience at the United States Forces-Iraq change of command ceremony on Sept. 1, 2010, at Iraq's Camp Victory. Gen. Lloyd Austin, USA, seated center, relieved Gen. Ray Odierno, USA, as the commander of USF-I. (Photo by Sgt. 1st Class Roger Dey/Army)

"General Austin got the job done. He played a crucial role in bringing 150,000 American troops home from the theater of war. Pulling that off took more than just the skill and strategy of a seasoned soldier," Biden wrote. "It required Austin to practice diplomacy, building relationships with our Iraqi counterparts and with our partners in the region. He served as a statesman, representing our country with honor and dignity and always, above all, looking out for his people."

Plitsas, who would later serve in several Pentagon roles and who now works as the vice chair of the Republican party in Fairfield, Connecticut and director of Connecticut GOP Vets, said he would have liked to see Biden choose "an intellectual sparring partner," rather than someone more likely to fall in line with him on most things.

"They were on the same page with a lot of issues; that counts a lot for President-Elect Biden," he said. "It's people he's worked with, whose viewpoints align with his, that he's worked with professionally."

Retired Army Lt. Gen. Mark Hertling, a classmate of Austin's at West Point and a supporter of President-elect Joe Biden, gave a ringing endorsement of Biden's surprise choice for SecDef, but did sound some notes of caution.

In a CNN appearance, Hertling said that Austin was a "very introverted, thoughtful, ethical and educated soldier" who would fit well within the confines of the military establishment, but would possibly need help in getting the department's message across to the civilian leadership and the public.

"As a combat veteran, he knows the issues," and has engaged with world leaders in serving as commander of U.S. Central Command, Hertling said.

Then-Vice Chief of Staff of the Army Gen. Lloyd Austin, left, speaks with troops at Combat Outpost Base Zangabad, Afghanistan, during a Thanksgiving visit in 2012. (Photo by Sgt. Ashley Curtis/Army)

However, "The downside, I think -- and I think Gen. Austin would admit this … he's very quiet," and might "leave to a deputy secretary" much of the outreach and media contacts.

"But he will stand up for what is right," Hertling said.

The pushback that arose immediately when Austin was reported to be Biden's SecDef pick has centered on his ties to industry -- he serves on the board of Raytheon -- and also on concerns that a recently retired four-star general leading the Pentagon went against the historic commitment to civilian control of the military.

"This is a Trumpian move," retired Army Lt. Col. Jason Dempsey, an adjunct senior fellow on military affairs at the Center for New American Security and Army veteran of Afghanistan and Iraq, said. He called Biden's choice of Austin an echo of President Donald Trump's pick of retired Marine Gen. Jim Mattis as his first SecDef.

By all accounts, Austin "was a helluva general," Dempsey said, but asked "why are we turning again to the military" to run the Defense Department.

But retired Army Gen. Barry McCaffrey, a Vietnam veteran who commanded the 24th Infantry Division (Mechanized) in the Gulf war, called the possible nomination of Austin "very good news for national security."

In a Twitter post, McCaffrey, an MSNBC contributor, said Austin was "a towering figure in the Armed Forces" who was "very easy to deal with" and "loved by the military."

The first signs that Biden was leaning away from Flournoy came on Nov. 24, when Biden introduced the initial picks for his national security team, but did not name a defense secretary pick.

The choice of Austin also followed concerns voiced by Rep. Jim Clyburn, D-S.C., that Biden might be overlooking qualified Black candidates in his Cabinet choices.

Clyburn, whose support of Biden in the South Carolina primary was crucial to propelling him to the Democratic nomination, said of Austin on MSNBC Tuesday morning that "I don't know him well," but he looked forward to working with him on diversity issues in the military.