As the US supreme court justice Clarence Thomas prepared to take questions from members of the rightwing legal advocacy group the Federalist Society, a few years back, he turned to the moderator.

Thomas joked that the nondescript man in the blue suit and white shirt was the “No 3 most powerful person in the world”, and then fell about laughing. The target of the judge’s mirth, Leonard Leo, grinned and remarked: “God help us.”

Yet both men understood at that moment in 2018 just how influential Leo was, in ways that few Americans knew. Most had never even heard of Leo, even though he was at that time instrumental in maneuvering Donald Trump to reshape the court on which Thomas sits, and so deliver one of its most politically sensitive rulings of recent times by overturning the right to abortion.

Leo, a 56 year-old whose opposition to abortion is rooted in his Catholic faith, remains an obscure figure to much of the US public, even after revelations that he heads a political group that has received an astonishing $1.6bn donation to push conservative causes, including election manipulation ahead of this year’s midterm votes.

Earlier this month the New York Times revealed that the money, said to be one of the largest single contributions to a political pressure group, arrived in a circuitous route from a figure who is equally obscure to most Americans: Barre Seid.

Seid, who has spent tens of millions of dollars funding conservative and libertarian organisations, donated an entire company last year to a newly founded political advocacy group run by Leo, the Marble Freedom Trust. Marble sold the firm, the Chicago electronics manufacturer Tripp Lite, this year for $1.6bn, according to tax records.

The roundabout process has prompted speculation Seid was sidestepping tax on the sale to maximize the funding for Leo.

The Marble Freedom Trust has already distributed nearly a quarter of a billion dollars, including $153m to the Rule of Law Trust to push the appointment of conservative judges. That still leaves more than $1bn to fund political causes close to Leo’s heart, including his interest in helping Republican officials manipulate elections ahead of the midterm vote and the next presidential ballot.

Leo defended the injection of a huge amount of “dark money” into the political process by claiming it merely levels the playing field against Democrats funded by liberal billionaires.

“It’s high time for the conservative movement to be among the ranks of George Soros, Hansjörg Wyss, Arabella Advisors and other leftwing philanthropists, going toe-to-toe in the fight to defend our constitution and its ideals,” he said in a statement.

Leo’s close relationship with Thomas goes back to 1991 when he worked to gather evidence to support the judge during his confirmation hearing for the supreme court.

Leo went on to work for the Federalist Society, founded in 1982 to counter what conservatives claimed was liberal dominance of US courts and law schools. He rose to become the society’s co-chair and oversaw the rise in its influence at the expense of the more liberal American Bar Association, in part through the effectiveness of his fundraising to back conservative judicial nominees.

As the conservative lawyer Ed Whelan wrote six years ago in the National Review: “No one has been more dedicated to the enterprise of building a supreme court that will overturn Roe v Wade than the Federalist Society’s Leonard Leo.”

In 2005, George W Bush nominated Harriet Miers, his deputy chief of staff, for a vacant seat on the supreme court. She was widely regarded as a weak candidate in any case, but when conservatives turned on her, and Miers withdrew, Leo saw to it that she was replaced by a figure far more acceptable to the right and opponents of abortion, Samuel Alito.

Senator Sheldon Whitehouse, one of the most outspoken critics of dark money’s influence on politics, told the Guardian earlier this year that was a turning point.

“It was at that point that the grip of this little donor elite and Leo, its Federalist Society operative, really took hold. Justice Samuel Alito was the product of that and he has proven himself on the court as being a faithful workhorse for that dark money corporate rightwing crew,” he said.

New opportunities presented themselves with Trump’s election in 2016.

Leo drew up a list of 11 potential supreme court nominees to help Trump, a man who had previously claimed to be pro-choice, woo conservative and evangelical voters by committing to nominate justices who were hostile to abortion rights.

After Trump’s victory, Leo took time away from the Federalist Society to work as an advisor to the president. All three of those eventually seated on the US’s highest court during Trump’s tenure and who voted to overturn Roe v Wade – Neil Gorsuch, Brett Kavanaugh and Amy Coney Barrett – were named on the list Leo drew up during the campaign.

Now Leo has turned his attention to pushing conservative moves to manipulate elections in favour of Republicans through the Honest Elections Project, a recent addition to a web of interlinked groups funded with dark money, including from the libertarian Koch brothers.

Among other things, Leo is pushing a contentious legal theory that the US constitution gives state legislatures the power to decide how to run elections without intervention from the courts. The Honest Elections Project has made multiple legal submissions on the issue with the aim of removing the power of state courts to block gerrymandering and voter suppression measures to manipulate elections.

Earlier this year, Leo told the Washington Post that in using dark money for political ends he is not doing anything that has not been done before.

“Let’s remember that in this country, the abolitionist movement, the women’s suffrage movement, the American Revolution, the early labor movement, the civil rights movement of the 1950s and 1960s were all very much fueled by very wealthy people and oftentimes wealthy people who chose to be anonymous. I think that’s not a bad thing. I think that’s a good thing,” he said.