Private heiress who made Trump
SHE'S the publicity-shy billionaire who helped turn Donald Trump from novelty candidate into the President of the United States.
But after the release of a book that has infuriated the White House, the heiress has been forced to pick a side in the ugly public spat between Mr Trump and his former chief strategist Steve Bannon.
Rebekah Mercer and her billionaire father Robert Mercer were influential mega-donors to Mr Trump's presidential campaign and, according to Mr Bannon, "laid the groundwork for the Trump revolution".
The dad-and-daughter team almost never speak to the media so when Ms Mercer released a statement publicly bashing Mr Bannon last week, it showed just how deep the rift between Mr Trump and Mr Bannon had become.
Mr Bannon drew the ire of the President after he was quoted slamming his son Don Jr and daughter Ivanka in the scandalous book Fire And Fury: Inside The Trump White House by Michael Wolff.
After Mr Bannon's comments became public, Mr Trump released an extraordinary official statement to say that his former top political adviser had "not only lost his job, he lost his mind".
It has been reported that after Mr Bannon's embarrassing comments in the book were revealed, the White House sent its top lieutenants out to trash the former insider's reputation in public.
Ms Mercer was inspired to do the same after speaking to Mr Trump over the phone on Thursday afternoon, the Daily Beast reports.
"I support President Trump and the platform upon which he was elected," Ms Mercer said in the statement.
"My family and I have not communicated with Steve Bannon in many months and have provided no financial support to his political agenda, nor do we support his recent actions and statements."
The public falling out is significant because the Mercers and Mr Bannon have conspired for more than five years to push a conservative, anti-establishment agenda - and install an outsider in the Oval Office.
WHO IS REBEKAH MERCER?
Ms Mercer has been dubbed "the First Lady of the alt-right" by conservative news publisher Christopher Ruddy.
Described by people who know her as "smart", "aggressive" and "ardently conservative", she is the middle daughter of Robert Mercer, a computer scientist and hedge-fund billionaire.
She runs the Mercer Family Foundation, which awards millions of dollars in grants to conservative organisations, and is a key financial backer of right-wing website Breitbart News.
While Mr Trump boasted that he was funding his own presidential campaign - as a way to prove he was not beholden to special interests - the truth is that his run for the White House was accelerated by the Mercer family's riches.
"It would be difficult to overstate Rebekah's influence in Trump world right now," a Republican fundraiser told Politico after the election.
"She is a force of nature. She is aggressive and she makes her point known."
During the transition, she pushed for Mr Trump to appoint conservative figures to key roles, such as advocating for Jeff Sessions as attorney-general, and brought in Mr Bannon and Kellyanne Conway for key roles.
Ms Mercer, 44, had a middle class upbringing in Westchester County, New York, studying at Stanford University before her father Robert struck it rich working at the hedge fund Renaissance Technologies.
They now have money to spare: Mr Mercer has a baby grand piano on his yacht, and when Ms Mercer and her sisters heard that a bakery in Manhattan that produced their favourite biscuits was going under, they swooped in and bought out the whole business.
While she has used her family's millions to greatly influence the national political landscape - pushing a small government, pro-individual freedom, anti-mainstream media, anti-establishment agenda - she remains intensely private. She is known for working from her $28 million ($A35 million) Upper West Side apartment, where she homeschools her four children.
Ms Mercer and her father show up numerous times in the infamous Fire And Fury book.
Wolff says Mr Trump "sold his losing campaign" to the Mercers in August 2016, when they offered to inject $5 million ($A6.4 million) to turn his dire poll numbers around. The family and Renaissance Technologies would go on to donate $23.7 million ($A30.2 million) to Republican campaigns during the 2016 election, according to the Centre for Responsive Politics.
"Theirs was a consciously quixotic mission. They would devote vast sums - albeit just a small part of Bob Mercer's many billions - to trying to build a radical free-market, small-government, homeschooling, anti-liberal, gold-standard, pro-death-penalty, anti-Muslim, pro-Christian, monetarist, anti-civil-rights political movement in the United States," Wolff writes.
According to The Washington Post, the Mercers and Mr Bannon had plotted to groom an outsider candidate for the presidency as far back as 2011, well before Mr Trump announced his candidacy.
The family had funded research that showed that voters were sick and tired of Washington elites from both major parties, and Mr Trump became the perfect vehicle for their anti-establishment uprising.
While Mr Mercer earned the fortune, Wolff handed the purse strings for political activism to his daughter, who is the true hard-line conservative.
"It was Rebekah Mercer - who had bonded with Bannon, and whose politics were grim, unyielding, and doctrinaire - who defined the family," Wolff writes.
A senior White House staffer said in the book that Ms Mercer was "nuts … full-fledged - like, whoa, ideologically there is no conversation with her".
THE DANGER FOR DONALD TRUMP
Robert and Rebekah Mercer have reaffirmed their support for Mr Trump since the book was released, despite the fact that Mr Trump is quoted as calling them "wackos" in it.
Mr Mercer is notoriously awkward, more comfortable in front of a computer than looking someone in the eye.
He once told a friend he preferred the company of cats to humans, according to The Wall Street Journal.
"Bob believes that human beings have no inherent value other than how much money they make," an unnamed co-worker told the New Yorker. "If someone is on welfare, they have negative value. If he earns a thousand times more than a schoolteacher, then he's a thousand times more valuable."
Mr Trump also avoided being in the same room as Ms Mercer, according to Fire And Fury.
White House spokeswoman Sarah Huckabee Sanders maintained last week, however, that Mr Trump's relationship with the Mercer family was "good".
The great challenge for Mr Trump is keeping the Mercers on side, given that they still have major influence over Breitbart, where his strongest supporters get their news.
"Trump's victory had, in some sense, handed the Mercers the tool with which to destroy him," Wolff writes.
"As push came to shove and the mainstream media and swamp bureaucracy more and more militantly organised against him, Trump was certainly going to need the Mercer-backed alt-right standing up in his defence.
"What, after all, was he without them?"