White House chief strategist Steve Bannon is the latest top aide of President Donald Trump to leave his post.
Press Secretary Sarah Huckabee Sanders confirmed that Friday was his last day.
His exit follows a review of his position by White House Chief of Staff John Kelly.
Mr Bannon, a right-wing nationalist and former head of Breitbart.com, helped shape the "America First" message of Mr Trump's election campaign.
But critics had accused the 63-year-old of harbouring anti-Semitic and white supremacist views.
In another departure from Mr Trump's team, billionaire investor Carl Icahn announced he was ending his role as the president's special advisor on regulatory reform, after facing criticism that his advice could benefit his own businesses.
Mr Bannon is known to have competed for influence in the West Wing against more moderate factions, including members of the Trump family.
He told the Bloomberg TV network: "I'm leaving the White House and going to war for Trump against his opponents - on Capitol Hill, in the media, and in corporate America."
Mr Trump fuelled speculation when asked last week about Mr Bannon's future as he replied: "We'll see."
Mr Bannon's interview this week with the American Prospect, a liberal magazine, reportedly infuriated the president.
The White House aide was quoted as dismissing the idea of a military solution in North Korea, undercutting Mr Trump.
Mr Bannon told associates he thought it was an off-the-record chat and didn't realise he would be quoted.
Ms Huckabee Sanders' statement said: "White House Chief of Staff John Kelly and Steve Bannon have mutually agreed today would be Steve's last day.
"We are grateful for his service and wish him the best."
Source familiar with the decision said Mr Bannon had been given the chance to leave on his own terms.
Mr Bannon took over as chief of Trump's presidential campaign in August 2016.
He was formerly a US Navy officer, Goldman Sachs investment banker, Hollywood movie producer and head of Breitbart News.
He has reportedly told friends he could go back to the right-wing outlet that has boisterously supported Mr Trump.
In a potentially worrying sign for the White House, Breitbart's senior editor-at-large Joel Pollak tweeted: "#WAR".
Who else left Trump's White House team?
Anthony Scaramucci, communications director - 31 July
Reince Priebus, chief of staff - 28 July
Sean Spicer, press secretary - 21 July
Mike Dubke, communications director, 30 May
James Comey, FBI director - 9 May
Michael Flynn, national security adviser - 14 February