Lieutenant General Herbert Raymond “H.R.” McMaster was chosen to replace Michael Flynn as National Security Adviser for President Donald Trump. The 54-year-old McMaster, who earned the nickname “The Iconoclast General,” is a career Army officer who is still serving. He served in the Persian Gulf War and the wars in Afghanistan and Iraq.

Before becoming NSA, McMaster was the director of the Army Capabilities Integration Center and Deputy Commanding General, Futures at U.S. Army Training and Doctrine Command.

Senator John McCain praised Trump’s decision to pick McMaster for the job, calling him an “outstanding choice” and a man of “genuine intellect, character, and ability” who “knows how to succeed.”

“President, thank you very much. I would just like to say what a privilege it is to be able to continue serving our nation,” McMaster said when Trump introduced him. “I’m grateful to you for that opportunity, and I look forward to joining the national security team and doing everything that I can to advance and protect the interests of the American people. Thank you very much.”

McMaster has been married to Kathleen Trotter since 1985. They have three daughters, Katharine, Colleen and Caragh.

Here’s a look at McMaster’s life and career:

1. McMaster Wrote the Book ‘Dereliction of Duty,’ Criticizing Vietnam-Era Officers

In 1997, McMaster published Dereliction of Duty, a book that criticized the military officers of the Vietnam War era for not challenging President Lyndon B. Johnson and Secretary of Defense Robert McNamara over their Vietnam strategies. Surprisingly, the book is on the Marine Corps. reading list as suggested reading for colonels and generals.

Lt. Gen. H. R. McMaster: U.S. Policy Mistakes in the Vietnam WarLieutenant General H. R. McMaster describes a series of events that led to what he says was an American war in Vietnam that lacked strategy and failed to consider long term costs and consequences. This Carnegie Council event took place on December 4, 2014. For complete audio and transcript and video clips, go to: http://www.carnegiecouncil.org/studio/multimedia/20141204/index.html 2015-01-12T18:57:43.000Z

McMaster wrote the book for his University of North Carolina Ph.D. thesis. The book also remains highly influential in the Pentagon. According to a CNN report from 2006, Gen. Peter Pace, the chairman of the U.S. Joint Chiefs of Staff at the time, “considered the seminal work on military’s responsibility during Vietnam to confront their civilian bosses when strategy was not working.”

McMaster’s decorations include the Purple Heart, Silver Star, Legion of Merit, Bronze Star and Joint Service Commendation Medal. He also has medals from his service in Afghanistan, Iraq and the Global War on Terrorism. He also received a NATO Medal and Kuwait Liberation Medals from Kuwait and Saudi Arabia.

McMaster is remembered by many at his alma mater, UNC-Chapel Hill, as a “soldier scholar” when he was completing his doctoral dissertation. ““He is a straight shooter,” UNC professor Michael Hunt told the News-Observer. “He can listen, he can argue, he’s analytically sharp. He was just really on fire.”

2. McMaster Warned That the Army Is ‘Out-Ranged & Outgunned by Many Potential Adversaries’

Global Ethics Forum: The Future of the American Military with Lt. Gen. H. R. McMasterU.S. Army Lieutenant General H. R. McMaster tackles the pressing questions facing the military: How can U.S. soldiers be trained to maintain ethical and legal standards in today's complex and often brutal environment? How is the Army preparing for current and future conflicts? For full audio and transcript and video clips, please go to http://www.carnegiecouncil.org/studio/multimedia/20141204/index.html 2015-04-16T14:37:02.000Z

As a futurist within the Army, it was McMaster’s job to predict how the U.S. will do against future threats. In an April 2016 testimony before the Air-Land subcommittee of the Senate Armed Services Committee though, he warned that the Army is too small at this point and the shrinking needs to stop.

“We are out-ranged and outgunned by many potential adversaries,” McMaster said, reports Breaking Defense. “[And] our army in the future risks being too small to secure the nation.”

At the time of his testimony, there were only 980,000 soldiers in the Army. The Army Times later reported that the Army is at its smallest size since before World War II.

Preview Maj Gen HR McMaster interviewA preview of the Ledger-Enquirer interview with outgoing Fort Benning MCoE Commanding General, Maj. Gen. H.R. McMaster 2014-07-10T22:41:10.000Z

“As we look to the future sir, we think that risk will become unacceptable,” McMaster told Senators. Even today, “we’re having a harder and harder time for the smaller force to keep pace with increasing demand.”

The outspoken McMaster also warned that U.S. Army technology is falling behind. “The Bradley fighting vehicle and the Abrams tank will soon be obsolete… but they will remain in the Army inventory for the next 50 to 70 years,” he said.

McMaster is also concerned that Russia is ahead of the game in battle drones. As Defense One reported in September, McMaster said that the U.S. Army is playing catch-up in that area.

“This is a big area of focus. We’re looking at a whole family of unmanned systems from the very low squad level. What I’ve talked about as a priority is the squad at a foundational level,” said McMaster. “We need a number of platforms that we can deploy. We’re interested in vertical-takeoff-and-push capability” as well as drones that can fly autonomously, resist complex electromagnetic attacks.” The Army wants drones “that can be deployed from a vehicle and hover over a vehicle. We’re experimenting with all of these capabilities,” he said, reports Defense One.

3. McMaster Calls Cyber-Terrorism a ‘Significant Threat’

Lt. Gen. H. R. McMaster: Combatting ISIS with PoliticsLieutenant General H. R. McMaster believes U.S. efforts in Iraq failed to prepare Iraqi troops for a fight against ISIS because the military training and strategies failed to take into account the politics of these contested spaces. This Carnegie Council event took place on December 4, 2014. For complete audio and transcript and video clips,… 2015-01-12T18:57:43.000Z

In a 2014 interview with the Ledger-Enquirer, McMaster stressed the importance of the Army working together to face threats. His words could also apply to the political climate in Washington as well.

“We’ve got to work across the whole Army, because the future course of the Army is what 51 percent or more of the Army believes it is every day. So, you can’t work in a vacuum — you’ve got to work with everybody on it,” McMaster said.

In that same interview, McMaster was serious about the threat cyber-terrorism poses to the U.S.

Colonel H.R. McMaster | Charlie RoseColonel H.R. McMaster is known as one of the leading experts on counterinsurgency warfare in the U.S. military. In 2005-2006 he led the effort to clean out the restive city of Tal Afar in northwest Iraq, and he's recently served as an adviser to Gen. David Petraeus. Here's a look at a recent conversation I… 2008-06-02T16:32:22.000Z

“I think cyber-terrorism — espionage as we are learning — is a significant threat. The fact is the cyber-domain is a contested space every day already,” McMaster explained to the Ledger-Enquirer. “The key question is, how does this fit into the overall problems of future war?”

He continued, “I think the key thing for us is really going to be how we develop systems that are resilient, that are able to allow us to operate and communicate freely during operations. And then we have to learn how we disrupt enemy capabilities to affect us. I think we have some really great people working on this right now, but of course this is a relatively new area that we have to cope with.”

4. McMaster’s Success at the Battle of 73 Easting Was Included in a Tom Clancy Novel

Continuities and Change in Future Armed ConflictJake Tapper (moderator) – Chief Washington Correspondent; Anchor, The Lead, CNNLt. Gen. H.R. McMaster – Deputy Commanding General, Army Capabilities Integration Center, U.S. Army Training and Doctrine Command The First Annual Future of War Conference brings together a diverse, interdisciplinary collection of experts to discuss the profound social, political, economic, and cultural implications of the… 2015-03-03T14:50:37.000Z

One of the key battles in the Persian Gulf War McMaster participated in was the Battle of 73 Easting. He was a captain, commanding Eagle Troop of the 2nd Armored Cavalry Regiment. Even though his group was outnumbered by the Iraqi forces, their nine tanks easily defeated the enemy’s forces because they were using outdated technology.

In an essay for The Strategy Bridge, McMaster admitted that future wars will look very different from this nearly three-decade-old battle, but it still has lessons for today’s commanders.

“Although future battles will likely be fought against more capable enemies and under more challenging and complex conditions, there are lessons from battlefield victories twenty-five years ago that remain relevant to combat readiness today and in the future,” McMaster wrote. “Well-trained, confident platoons and companies provide the foundation for our Army’s and Joint Force’s ability to fight.”

McMaster’s success during the Battle of 73 Easting was included in the Tom Clancy nonfiction book Armored Cav.

5. McMaster Is a Student of Military History Who Sees Similarities in All Wars

Harbingers of Future War: Implications for the Army with Lieutenant General H.R. McMasterPlease join us for a discussion with Lieutenant General H.R. McMaster, Director, Army Capabilities Integration Center and Deputy Commanding General, Futures, U.S. Army Training and Doctrine Command Featuring: Lieutenant General H.R. McMaster, USA Director, Army Capabilities Integration Center and Deputy Commanding General, Futures, U.S. Army Training and Doctrine Command Moderated by: Dr. Kathleen H. Hicks… 2016-05-04T21:15:47.000Z

In a 2012 interview with McKinsey & Company, McMaster said that his interest in military history has been an influence on his career. Even though part of his current job is about looking to the future, there are factors of war that never change.

McMaster said in 2012 that one of the failures of the Iraq and Afghanistan policies was planning for “a sustainable political outcome that would be consistent with our vital interests, and it complicated both of those wars.”

He also noted that war is “an inherently human endeavor,” and that no matter how technologically advanced the U.S. is, there is still a human factor.

“We assumed that advances in information, surveillance technology, technical-intelligence collection, automated decision-making tools, and so on were going to make war fast, cheap, efficient, and relatively risk free—that technology would lift the fog of war and make warfare essentially a targeting exercise, in which we gain visibility on enemy organizations and strike those organizations from a safe distance. But that’s not true, of course,” McMaster explained to McKinsey & Company.

During an interview with TBO.com in April 2015, McMaster stressed the importance of knowing how people act and interact when predicting the future of war.

“What we have to do is really develop the ability to think clearly about future war,” McMaster explained in 2015. “And what we have to do is identify changes in the so-called human domain and understand what is fundamentally driving conflict, which is human in nature.”