Robert Mercer likes to describe himself as a mere computer programmer. In fact, his early work on artificial intelligence led to him create algorithms that would transform financial trading, making him a billionaire and a conservative donor who arguably did more than any other to put Donald Trump in power.
He speaks rarely in public – and never to journalists. As a result, his wealth and kingmaker status have taken on a near mythical status, only enhanced by his stake in Cambridge Analytica, the data analytics firm at the centre of a growing privacy scandal.
The foundations of his power come from his time at IBM Research, where he worked after completing a PhD in computer science at the University of Illinois.
But he made his mark on Wall Street when he joined the hedge fund Renaissance. It was the early 1990s and quantitative analysts were beginning to take over financial trading with complex mathematical models.
Mr Mercer's expertise in AI made him perfectly placed to build systems that could use tiny advantages in speed and knowledge to maximise profits.
Like so much of his life, how he did it remains secret. But today the 71-year-old is credited with making Renaissance one of the world’s most successful funds. One employee retirement fund made annual gains of more than 70 per cent up to 2014, according to Bloomberg.
His success saw him elevated to co-chief executive in 2009, acquiring the sort of wealth that allowed him to buy a $2.9m train set.
And with it came political influence.
Much of his money has been channelled through conservative organisations such as the Heritage Foundation. But some has also gone into more extreme projects, including a climate change denying think tank, the Heartland Institute, or efforts to disrupt mainstream media, with a reported $10 million stake in Breitbart News that enabled Steve Bannon to embark on his project of turning the website into an explosive, populist Huffington Post for the Right.
The site helped launch such incendiary figures as Milo Yiannopoulis and others in the alt-Right.
But Mr Mercer – along with his daughter Rebekah – may have reached the height of his powers in the 2016 US presidential election.
As well as donations from their political fund, the pair were instrumental in building Mr Trump's campaign. They introduced the New York property mogul to Mr Bannon, who would later become White House chief strategist.
Mr Bannon's greatest contribution may not have been his populist instincts and strategic brain but the “secret sauce” of his patron’s new technology firm that could identify the personality types of key swing voters, finding silent Trump supporters and delivering them to the ballot box.
Although Mr Mercer was only ever a passive investor in Cambridge Analytica – to the tune of a reported $15 million – his daughter sits on its board.