Stephen K. Bannon, President Trump’s White House chief strategist, was already set to become one of the most powerful people on the planet—even before Trump appointed him to the National Security Council last weekend.

Those who have known Bannon for years, and before he ascended to executive power, describe a man almost obsessed with military history, guerilla warfare, and the general art of war and nationalist foreign policy.

In his Hollywood days, Bannon could easily play war, writing vast landscapes of warfare and conflict into his scripts, sometimes set in outer space.

Thanks to Donald J. Trump, Bannon now could get to do it for real.

That’s because in a presidential memorandum this past weekend, Trump gave his chief strategist a permanent seat at the National Security Council table, while military and intelligence leaders were effectively downgraded. The move to elevate Bannon, a purely political adviser, was unusual to provoke outcry from even fellow Republicans.

For instance, Bannon has very limited experience in U.S. government, and has little relevant experience for the position. Bannon did serve seven years in the Navy several decades ago, before making his name in the private sector, conservative Hollywood, and then politics.

“This is literally the most terrifying thing that’s ever happened,” a former Hollywood associate of Bannon’s (who requested anonymity for fear of retribution, describing Bannon as “vindictive”) told The Daily Beast when discussing the new national-security position.

“He constantly used military terms, used military terms to describe people who worked for him… like, ‘grunts,’” one former Breitbart staffer recalled. “He always spoke in terms of aggression. It was always on-the-attack, double down... macho stuff. Steve has an obsession with testosterone.”

It’s a habit that will likely continue into his time in the executive branch. The New York Times reported that last week’s avalanche of Trump of executive orders was primarily hatched by Bannon and his team, and doubled as an effort “at disorienting the ‘enemy.’”

“If there’s one sort of movie theme that encapsulates Steve Bannon’s philosophy on this, it’s that line from Team America: World Police: ‘You have balls—I like balls,’” Ben Shapiro, former Breitbart editor-at-large, said.

Bannon and a spokeswoman did not respond to requests for comment on this story. He has, however (as The Daily Beast previously reported), described himself as a “Leninist,” with regard to his goals of political insurrection.

“Lenin wanted to destroy the state, and that’s my goal, too,” Bannon said at a book party in Washington, D.C., in November 2013. “I want to bring everything crashing down, and destroy all of today’s establishment.”

Lenin isn’t the only communist military or political victor who Bannon seemed to admire, for tactics and ruthlessness, if not leftist ideology. Bannon did not write very many articles at Breitbart, but one of the pieces that bears his byline is an October 2013 obituary for the “‘Red’ Napoleon” of the Vietnam War: Gen. Võ Nguyên Giáp, a famous commander of the Vietnam People’s Army who (like Bannon) once worked in journalism before defeating entrenched establishment powers.

“Giap’s tenacity and ruthlessness became his trademarks as he fought two of the world’s most technologically advanced militaries,” Bannon wrote.

You can also find Bannon’s affection for military and strategic ruthlessness in what he reads. According to two of Bannon’s former friends from his West Coast days, two of his favorite books are Sun Tzu’s The Art of War, the hugely influential ancient Chinese text on military strategy, and the Hindu Bhagavad Gita. The latter tells the story of a holy war to establish dharma.

Julia Jones, Bannon’s longtime Hollywood writing partner and former close friend, recalls seeing him excitedly flipping through both books, and talking about them lovingly and often. She would frequently see various “books all over [Steve’s place] about battles and things,” among his clutter of possessions and interests. (Late last year, Jones—who identifies as a “Bernie Sanders liberal”—had a falling out with Bannon due to his work on the Trump presidential campaign, a role that she said absolutely “disgusted” her.)

“Steve is a strong militarist, he’s in love with war—it’s almost poetry to him,” Jones told The Daily Beast in an interview last year, well before Trump won the election and Bannon landed his new job. “He’s studied it down through the ages, from Greece, through Rome... every battle, every war… Never back down, never apologize, never show weakness… He lives in a world where it’s always high noon at the O.K. Corral.”

Jones said that Bannon “used to talk a lot about dharma—he felt very strongly about dharma... one of the strongest principles throughout the Bhagavad Gita.”

She also noted his “obsession” with the military victories and epic battles of the Roman Empire’s Marcus Aurelius and Julius Caesar. But a personal favorite of Bannon’s was the subject of the Peloponnesian War fought between Athens and Sparta.

“He talked a lot about Sparta—how Sparta defeated Athens, he loved the story,” Jones said. “The password on his [desktop] computer at his office at American Vantage Media in Santa Monica was ‘Sparta,’ in fact.”

This is the mindset of Trump’s top White House aide who just earned himself a seat at the table on the National Security Council. Regarding foreign policy and national security, Bannon has a few top priorities: He favors “aggressive military action” to defeat Islamist terror networks (action he thought was lacking during the Obama administration), and wants to build strong ties with far-right, nationalist political parties across Europe.

“He has long wanted to work with all of those parties, but that was only in promoting them with Breitbart,” a source close to Bannon told The Daily Beast in November. “Now he has the power of the White House to do it.”

Those who remain and become Bannon’s closest allies on issues of national security and foreign policy will most likely end up being whoever Bannon sees as tough and ruthless—much in the same way he sees himself and his preferred military leaders of history.

“‘Hammer’ was one of his favorite words,” a former Bannon associate (another person requesting anonymity for fear of reprisals) told The Daily Beast. “‘You’re a hammer,’ he’d say if he really liked you… if you’re ruthless.”