By Kaitlan Collins, CNN

(CNN) -- Moments before President Donald Trump entered the room for his recently reinstated daily coronavirus briefing Monday, three aides preceded him: Treasury Secretary Steven Mnuchin, budget chief Russell Vought and a new face.

"Wait, by the way, the gentlemen -- you know everybody ... This is Scott Atlas. Do you know that?" Trump asked.

The man Trump was pointing to was Dr. Scott Atlas, a fellow at Stanford University's Hoover Institution who frequently appears on Fox News and has advised Republicans in the past. And crucially, unlike the government's medical experts who have advised Trump until now, has adopted a public stance on the virus much closer to Trump's -- including decrying the idea that schools cannot reopen this fall as "hysteria" and pushing for the resumption of college sports.

Several months into the pandemic sweeping the nation, Atlas made his debut in the briefing room with a new title: adviser to the President.

"He's working with us and will be working with us on the coronavirus," Trump said. "And he has many great ideas. And he thinks what we've done is really good, and now we'll take it to a new level."

In a statement on his hiring, White House spokesman Judd Deere called Atlas "a world renowned physician and scholar of advanced medical care and health care policy" who has been brought in "to help defeat this virus from China. We are all in this fight together, and only the media would distort and diminish Dr. Atlas' highly acclaimed career simply because he has come to serve the President."

With the coronavirus spreading largely unchecked across the US, Trump has called on hesitant governors to reopen their states and school administrators to put children back in the classroom. Though Trump believed his push would help woo suburban voters, some districts have increasingly pivoted to virtual models while others, such as some school districts in Georgia, have opened only to see a cluster of new cases.

Atlas has been an extensive critic of severe lockdowns and publicly agreed with the President on all of those above measures. He joins Trump's team at a time when he finds himself increasingly at odds with the other medical experts in his administration, such as Dr. Anthony Fauci and Dr. Deborah Birx.

Although Monday was Trump's first public introduction of Atlas, multiple sources with knowledge of the relationship told CNN that Atlas has been informally advising Trump for weeks. Trump first noticed Atlas on Fox News, where he asserted it doesn't matter "how many cases" there are in the US, wrongly claimed those under 18 years old have "essentially no risk of dying," implied teachers who are at high risk for contracting Covid-19 should "know how to protect themselves," baselessly claimed "children almost never transmit the disease" and without evidence blamed a rise in cases in southern states on protests and border crossings.

"I'm an adviser," Atlas said on Fox News Monday night when asked about his new role. "I was asked by the President to advise him and it's obvious that the answer is, 'Yes, sir, and any way I can help I will do so.' "

A trained medical doctor who attended the University of Chicago School of Medicine, Atlas has advised Republicans in the past, including Rudy Giuliani, the President's personal attorney who has also fanned conspiracy theories about coronavirus. Now Atlas will serve as an adviser to the President who works out of the Executive Office Building next door to the White House. (The White House declined to say whether Atlas was receiving a taxpayer-funded salary.)

Several of the President's allies welcomed Atlas to his team, viewing him as a voice with medical credentials that agrees with their skepticism of guidance and advice from experts such as Fauci and Birx. On his radio show this week, Rush Limbaugh praised Atlas and said "he is countering Fauci."

But Atlas isn't only seen as someone who can counter the medical opinions of the nation's top infectious disease expert. Trump has also recently grown disillusioned with the medical advice of Birx and has voiced skepticism about her ever since she praised House Speaker Nancy Pelosi in an interview after Pelosi criticized her. Two officials voiced concern that Trump brought Atlas in several months into the pandemic to diminish the voices of medical experts he disagrees with.

Several of the health professionals on the task force raised questions about Atlas, asking each other who he was and what his role would be.

Atlas appears to have settled into his new position quickly. He recently joined other officials for an outing at the Trump Hotel, has been on several calls to strategize the administration's response and even led another by himself, two sources said. He is also expected to appear at an event on reopening schools with the President Wednesday.

But it was the message Trump sent by bringing Atlas to two coronavirus briefings this week that resonated the most with the rest of the task force. When the President initially revived his daily briefings, he told aides he did not want the experts who had at times contradicted him to join him any longer. Instead, he claimed, he would relay the administration's message that day by himself. (Birx sat to the side during one briefing.)

This week Atlas has already attended two briefings, though he hasn't been given a speaking role.