President Trump announced Monday that Army Lt. Gen. H.R. McMaster, a well-known strategic thinker who has warned of the risks of shrinking the Army, will be his next national security adviser.

McMaster replaces retired Lt. Gen. Mike Flynn, who was fired a week ago after news broke that he had misled Vice President Mike Pence about his communications with Russian ambassador to the United States Sergey Kislyak before the inauguration.

Making the announcement from his Mar-a-Lago estate in Florida, Trump also revealed that retired Lt. Gen. Keith Kellogg will remain as the chief of staff for the National Security Council.

"That combination is something very, very special," Trump said of McMaster and Kellogg, who has been acting national security adviser since Flynn's departure.

McMaster "is a man of tremendous talent and tremendous experience, and I have read a lot over the last two days — he is highly respected in the military and we're very honored to have him," Trump told reporters.

Trump made the announcement before reporters while seated between Kellogg and McMaster on a couch at the estate.

"I'd just like to say what a privilege it is to be able to continue serving our nation and I'm grateful to you for that opportunity," McMaster said. "And I look forward to joining the national security team in doing everything I can to advance and protect the interests of the American people."

McMaster, 54, is a career officer in the Army, which he joined in 1984 after graduating from West Point, and is widely considered to be one of the service's top strategic thinkers.

Since 2014, McMaster has served as the director of the Army Capabilities Integration Center and as deputy commanding general, Futures, U.S. Army Training and Doctrine Command.

In April 2014, McMaster made Time magazine's list of 100 most influential people in the world, being hailed as "the architect of the future U.S. Army."

McMaster served in the Gulf War, and has held senior roles in the Iraq and Afghanistan wars.

Perhaps one of McMaster's more controversial roles was that of author of the 1997 book Dereliction of Duty. In the book, written as part of his PhD dissertation, McMaster criticized President Lyndon B. Johnson and his administration's military strategy during the Vietnam War.

Sen. Tom Cotton, R-Ark., and an Army veteran, hailed Trump's decision. "H.R McMaster is one of the finest combat leaders of our generation and also a great strategic mind," Cotton said in a statement. "He is a true warrior scholar, and I'm confident he will serve both the president and the country well."

More recently, McMaster has sounded the alarm over proposed cuts to the Army and the service's ability to carry out its missions.

Sen. John McCain, R-Ariz., quoted McMaster during a hearing in April in which he discussed proposed force cuts, calling McMaster "an individual known to all of us as one of the wisest soldiers."

"By the end of the next fiscal year," McCain's opening statement said, "the Army will be cut down to 450,000 active-duty soldiers, down from a wartime peak of 570,000. These budget-driven force reductions were decided before the rise of ISIL or Russia's invasion of Ukraine. Ignoring these strategic facts on the ground, the budget request continues down the path to an Army of 450,000 soldiers, an Army that General H.R. McMaster testified earlier this week 'risks being too small to secure the nation.' "

McCain's praise was just as abundant on Monday, calling McMaster "an outstanding choice."

"I have had the honor of knowing him for many years, and he is a man of genuine intellect, character and ability," McCain said. "He knows how to succeed. I give President Trump great credit for this decision, as well as his national security Cabinet choices. I could not imagine a better, more capable national security team than the one we have right now."

McMaster's selection comes after a rocky week for the National Security Council, beginning with Trump's firing of Flynn. Following reports from administration sources that Flynn had discussed sanctions with Kislyak before President Obama imposed them, Flynn assured Pence that sanctions didn't come up. Pence later learned that wasn't the case after a spokesman said it's possible Flynn had indeed discussed the sanctions.

Almost immediately after the firing, a series of retired senior military officers' names were floated as successors. On Thursday, Trump's top pick, retired Navy Vice Adm. Robert Harward rejected Trump's offer, saying he wanted to focus on his family on his finances. Other reports, however, said he was turned off by the level of chaos he saw in the administration. Another officer frequently mentioned, retired Gen. David Petraeus, took his name out of the running.

Unlike the other men in contention, McMaster is still on active duty, which is not unprecedented for this position. Colin Powell was still an Army general while serving as President Reagan's national security adviser in 1987.