But for Trump administration insiders, Bannon's appointment was little more than a natural evolution of his status as one of the President's most trusted and influential advisers.
That's because Bannon's role has long eclipsed that of traditional political strategist, with the former head of the right-wing Breitbart News site quickly taking custody of Trump's political and policy agendas
not just as tactician, but as one of its chief architects.
That role will now officially extend to crafting the Trump foreign policy
, placing a firebrand who has repeatedly targeted the Republican establishment and called for a radical reshaping of the US' role in the world in a prime position to reshape the current world order -- not just for the term of Trump's presidency, but for decades to come.
Already in just the first week of Trump's presidency, Bannon has steered Trump toward implementing many of the course-altering foreign policy actions Trump touted during the campaign, with Trump signing a series of executive actions to torpedo the Trans-Pacific Partnership free trade deal, order the construction of a massive border wall and temporarily ban citizens of seven Muslim-majority countries while also suspending admissions of refugees into the US.
Bannon was a particularly formidable force on the latter, overruling -- with White House policy director Stephen Miller -- the Department of Homeland Security's more narrow reading of Trump's executive order by directing federal officials to also bar green card holders from one of those seven countries from entering the US. Those legal US permanent residents will now need to apply for a waiver to leave and return to the US, for at least the next 90 days.
The flood of first-week actions are typical of Bannon's style, whose modus operandi is to always be on the offense, people familiar with his thinking said.
"He wants to flood the zone," a person who has worked with Bannon said. "If you can move fast to overwhelm the opposition, you'll get a lot more gains than if you do it incrementally ... That's pure Bannon. It's taking on real and imagined enemies and overwhelming them with stuff."
Bannon declined to be interviewed for this story.
The executive actions, though, are just an opening volley in a string of actions Bannon is revving up to implement as he looks to tailor US foreign policy to his ideology -- and his seating on the National Security Council now gives him the direct access he needs to shape the most sensitive national security discussions.
Already Bannon, a largely obscure figure during much of the campaign, has been an increasingly visible figure at Trump's side, whether it's sitting in the Oval Office while Trump speaks by phone with Russian President Vladimir Putin or across the table in the State Dining Room with congressional leaders.
Amid a fury of criticism even from some members of the President's party, White House press secretary Sean Spicer sought to downplay Bannon's role on the NSC on Monday, insisting Bannon is "not going to be in every meeting."
But his appointment is a sign of Trump's trust in the top adviser and a sign that he wants Bannon to be his eyes-and-ears in the top level meetings, said Jason Miller, a former top communications adviser to the Trump campaign and transition.
"He has the President's ear. It only makes sense to have him in this role listening to what's going on so he, too, can report back to the President," Miller said. "He also has such a keen understanding of the President's voice."
Bannon's ideology is one that frequently jibes with Trump's thinking on everything from combatting jihadist terrorism to better protecting the US from the economic whiplash of globalism and free trade deals -- at the risk of isolating the US.
But despite the overlap in the two men's worldview, Trump is no ideologue. Bannon, by contrast, is arguably the most ideological member of Trump's inner circle of top advisers and now finds himself in the position of filling that vacuum -- and fleshing out Trump-ism with his own philosophy.
While Trump arrived at his populist viewpoint seemingly by instinct, Bannon became the "economic nationalist" he now calls himself through a decades-long intellectual pursuit -- one that took him through the pages of history and philosophy books that have profoundly impacted his worldview.
Bannon has often leaned on history to argue for more extreme measures to counter "radical Islamic terrorism," arguing the "Judeo-Christian West" is once again facing a "crisis" akin to the battles Europeans waged to fend off assaults by Muslim armies. It's an ideology he's since worked to spread in the US and abroad, through the Breitbart News platform, which has run Islamophobic stories and race-baiting headlines.
Beyond US counterterrorism policy, Bannon is poised to be a driving force behind the radical reshaping of the US's trade policy and its attitude toward China.
The death knell to TPP last week was little more than a warning shot signaling to the world that Trump was serious about following through on the protectionist rhetoric that helped him win the presidency and Bannon, who has often cited his blue-collar roots, is gearing up to help craft those policies in line with his goals of shaping a movement that continues to draw the union workers who flocked to Trump's candidacy in 2016 and can outlast Trump's presidency.
And he is taking his most outsized role in the administration's foreign policy by helping to drive discussions on US-China policy. Privately, he has pushed to implement the border tariff Trump threatened during the campaign and invited comparisons between Trump's populist inaugural address with its "America First" proclamation and the Chinese President's defense of globalization just days earlier.
While Bannon has no significant foreign policy experience that would earn him a seat on the National Security Council, he is a former US naval officer who worked on the Naval Operations staff at the Pentagon and the former Goldman Sachs banker and hedge fund manager is well-versed in economic issues and global trendlines.
Miller, the former Trump spokesman, argued Bannon is "one of the leading national experts on this global trend of economic populism and economic nationalism we're seeing all across the entire world."
"Issues of economic geopolitical stability are national security issues also," Miller said.