Washington (AFP) - He is a reclusive hedge fund billionaire who made a fortune using complicated algorithms to bet on things other people could not see.

One of his gambles was on Donald Trump.

And his backing of the long-shot presidential candidate has made Robert "Bob" Mercer, the former co-CEO of Renaissance Technologies, the top powerbroker in Republican politics today.

The Mercer family is not nearly as well known as the industrialist Koch brothers or the Las Vegas casino magnate Sheldon Adelson when it comes to supporting right-wing causes in the United States.

And they are more than happy to keep it that way.

Mercer, 71, who worked as a computer scientist at IBM before joining Long Island-based Renaissance Technologies, has always shunned the limelight.

According to numerous accounts, Mercer is socially awkward and intensely private.

He is described in Michael Wolff's bombshell new book "Fire and Fury" as "almost nonverbal, looking at you with a dead stare and either not talking or offering only minimal response."

In November, Robert Mercer abruptly announced that he was stepping down as co-chief executive of Renaissance Technologies because of the unwanted press scrutiny brought about by his political activities.

In his resignation letter, Mercer also made his most expansive public comments to date, outlining the core principles of his libertarian philosophy.

- Advocate of small government -

"I believe that individuals are happiest and most fulfilled when they form their own opinions, assume responsibility for their own actions, and spend the fruits of their own labor as they see fit," he said.

"This is why I support conservatives, who favor a smaller, less powerful government."

In his book about the Trump White House, Wolff expanded further on what he claimed was the Mercer family doctrine.

He said they were attempting to build a "radical free-market, small-government, home-schooling, antiliberal, gold-standard, pro-death penalty, anti-Muslim, pro-Christian, monetarist, anti-civil-rights political movement in the United States."

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With the silver-haired Mercer patriarch remaining behind the scenes, it is up to Rebekah, 44, the second of his three daughters, to channel the family money to conservative causes and maintain the direct line to the White House.

While the Koch brothers and other Republican mega-donors sat out the 2016 presidential race because of a distaste for Trump, the Mercers threw their considerable resources behind the brash real estate tycoon after initially backing Texas Senator Ted Cruz.

They donated millions to Trump's coffers and persuaded his then floundering campaign to take on board two figures seen as instrumental to his upset victory over Democrat Hillary Clinton -- anti-establishment ideologue Steve Bannon and pollster Kellyanne Conway.

Robert Mercer, who reportedly has an abiding hatred of the Clintons, is a long-time patron of Bannon, who headed the right-wing website Breitbart News until becoming chief executive of Trump's election campaign.

When President Trump angrily severed ties with Bannon recently over comments he made in the Wolff book, it was a damaging blow to his former White House chief strategist.

But the coup de grace to any remaining political ambitions Bannon may have had came a few days later, when the Mercer family pulled the plug on their long-time ally.

- 'I support President Trump' -

"I support President Trump and the platform upon which he was elected," Rebekah Mercer said in a rare public 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 excommunication marked the end of the long-standing collaboration between the Mercer family and Bannon, who had been a fringe player in Republican politics until a $10 million investment by the Mercers turned his Breitbart News into a powerful conservative voice.

The Mercers are estimated to have contributed a total of more than $100 million to conservative causes over the past decade, including funding for the Government Accountability Institute (GAI).

Rebekah Mercer serves as chairwoman of the board of the Florida-based institute co-founded by Bannon whose stated mission is to root out "cronyism and corruption."

GAI is perhaps best known for a 2015 book by its president, Peter Schweizer, that was highly critical of the Clintons: "Clinton Cash: The Untold Story of How and Why Foreign Governments and Businesses Helped Make Bill and Hillary Rich."

Besides contributing to Breitbart and GAI, the Mercers also invested in Cambridge Analytica, a political data analysis firm whose efforts have been credited with helping Trump win the 2016 election.

While Bannon has been the Mercers' frontman for their political activities for years, his departure from the scene would not appear to lessen their influence.

According to The Daily Beast, before repudiating Bannon, Rebekah Mercer held a telephone call with the White House, where she spoke with President Trump.