The most powerful recruiter in the world: How one man handpicked one-third of the Supreme Court
But Leo, the executive vice-president of the conservative Federalist Society, has likely done more than any other person to shape the Supreme Court and the federal bench, and as a result, the future of law and policy in the United States.
As the longtime leader of the most powerful network of conservative lawyers in the country, Leo is "a convener and a networker" who finds and cultivates influential Republican lawyers and judges, The New Yorker wrote in a recent story.
Last spring, Trump called on Leo to produce a list of Supreme Court nominees that the Trump campaign would make public as a way to expand the Republican candidate's appeal among conservative voters - something no presidential campaign had ever done before.
As Leo told The New Yorker, Trump gave him relatively loose guidelines: he wanted candidates who were very well qualified, "respected by all, not weak," and who would "interpret the Constitution the way the Framers meant it to be."
So Leo put together a list of nominees that would eventually include the 10th Circuit judge, Neil Gorsuch, who was sworn in as the Supreme Court's newest member on Monday, replacing the late conservative justice Antonin Scalia.
This is not the first time Leo has successfully shepharded a conservative judge onto the Supreme Court. Under George W. Bush, Leo was key in facilitating the nominations of John Roberts, now the Court's chief justice, and Samuel Alito, another conservative justice - in part by organizing public relations campaigns to promote them, as he did with Gorsuch.
Leo, 51, has spent his entire 26-year-long legal career at the Federalist Society, whose goal is to promote free-market and limited government principles. Many of its members, like Leo, who is a devout Catholic, have strong religious beliefs, according to The New York Times.
The Society was founded in 1982 by three law students at the University of Chicago and Yale, who were advised by Scalia, then a professor at Chicago, and Yale law professor Robert Bork, whose 1987 nomination to the Supreme Court by President Ronald Reagan was rejected by the Senate.
The group quickly found strong financial support in the form of powerful conservative donors, including Charles and David Koch and the Mercer family, which has donated large amounts to Trump's campaign and helped found Breitbart News. These days, its funding also comes from corporations,including Google and Chevron.
Thirty-five years later, the Federalist Society continues to cultivate its large membership among the law profession's youngest members.
"The key was to figure out how to develop what I call a 'pipeline'-basically, where you recruit students in law school, you get them through law school, they come out of law school, and then you find ways of continuing to involve them in legal policy," Leo told The New Yorker.
The Society's power and influence is unmatched by any similar liberal organization - its budget is more than three times that of the American Constitution Society, its left-leaning counterpart, according to The New Yorker.
While the Federalist Society describes its membership as "pro-constitution" originalists committed to literalist interpretations of the law, liberals see the group as having an activist anti-government agenda and "propagating an approach to understanding the Constitution that conveniently always [leads] to conservative outcomes," Caroline Fredrickson, the president of the American Constitution Society, told The New Yorker.
Over the next four years, Trump will likely have more federal court openingsto fill than any president in the last 50 years, including between one-third to one half of all appeals court judgeships.
And given that three of the Supreme Court's liberal justices are over 75 years old, Leo may get the chance to tilt the ideological balance of the Court with another nomination.
"There will be an opportunity for a transformation of the federal bench," Leo told The New York Times in March.