– Leonard Leo, a vice president of the conservative Federalist Society, will soon have his own grateful bloc of ideological allies on the Supreme Court.

Since the 1990s, he has been one of the most important inside players in the conservative legal movement and the man to see for those who aspire to sit on the nation’s highest courts.

Leo has been a longtime friend and champion of Justice Clarence Thomas, and he played a crucial role in promoting the two most recent GOP appointees to the high court: Justices Samuel Alito and Neil Gorsuch.

And Monday, President Donald Trump is expected to nominate another new justice from the shortlist prepared by Leo and the Federalist Society.

It is quite an accomplishment for a young lawyer who came to Washington not for money or prestige, but instead to transform the Supreme Court and to bring it in line with conservative principles, including ending a court-created right to abortion.

“No one has been more dedicated to the enterprise of building a Supreme Court that will overturn Roe vs. Wade than the Federalist Society’s Leonard Leo,” Ed Whelan, a former clerk for Justice Antonin Scalia and president of the Ethics and Public Policy Center, wrote in December 2016, shortly before Trump nominated Gorsuch to fill Scalia’s seat.

For his part, Leo, 52, downplays the talk of overturning abortion rights. “The left has been using Roe vs. Wade as a scare tactic since 1982,” he said in a recent TV interview. “This is not about overturning a particular case. It’s about getting the Constitution right.”

Leo’s detractors scoff at such claims and predict that a solidly conservative court will target liberal rulings.

Leo is always careful to emphasize that Trump is in charge of the court selection process, with the assistance of White House Counsel Don McGahn, who describes himself as a proud member of the Federalist Society. Leo describes the task of his group and the Heritage Foundation as one of screening judges to find the best thinkers and writers who adhere to the principles of “textualism” and “originalism” that are favored on the right.

This is not an academic exercise, however. Coming out on the wrong side in a highly charged case — like with the dispute over President Barack Obama’s health care law — could knock any Republican judge out of ­contention.

In interviews, Leo often speaks of his Roman Catholic faith and of the role it plays in his daily life. He and his wife, Sally, have had seven children. Their first, Margaret, was born with spina bifida. She used a wheelchair for mobility and suffered from medical problems, but he has said she had a spirit that lifted her family. Since her death in 2007, Leo says he has gone to mass daily.

He first gained attention in 2005 when he played a key role in elevating a little-known judge from New Jersey. Samuel Alito had served on the Third U.S. Circuit Court of Appeals for 15 years and had compiled a record as a smart and reliable conservative. Though Alito had served as a lawyer in the Reagan administration, he was not a familiar name to many in the Washington legal community. He was, however, known and admired by Leo.

Filling O’Connor’s seat

In early October 2005, President George W. Bush announced he was nominating White House Counsel Harriet Miers to fill the seat of retiring Justice Sandra Day O’Connor. But leaders of the conservative legal movement objected loudly, labeling her as unprepared and unreliable.

Bush retreated and withdrew her nomination at the end of the month. Four days later, he announced he was nominating Alito. In the 12 years since then, Alito has been a steady, predictable conservative. When the court has been split, he has not joined with the liberals in any case of ­significance.

Leo’s role has grown since Trump took office. The president promised repeatedly on the campaign trail that he would name conservative, “pro-life justices” to the high court, but he did not have a deep and experienced team of legal advisers.

Leo and the Federalist Society were prepared. A few days after Trump’s surprise election victory, Leo was at Trump Tower in New York offering his thoughts on how to proceed in filling the seat left vacant by Scalia’s death.

During the campaign, Trump took the unusual step of announcing he would choose his Supreme Court nominees from two lists that together included 20 judges or lawyers. Since then, a third list added five more people. Although the outside groups prepared the lists, Leo says Trump deserves the credit.

“This was his idea,” he said. “He had three criteria. He wanted people who were extraordinarily well-qualified. People who were not weak. And he wanted people who would interpret the Constitution as the framers meant it to be interpreted.”

The exit interviews of 2016 voters suggest Trump’s emphasis on conservative judges helped him win over those who were wavering or undecided.

With the first vacancy, both Leo and White House lawyers favored the idea of nominating a judge who had a significant track record of conservative rulings. Gorsuch, a Supreme Court clerk for Justice Anthony Kennedy, had served on the 10th U.S. Circuit Court of Appeals in Denver since 2006. He was an excellent writer and echoed Scalia’s approach to deciding cases.

This time, two of the top three candidates have a similar appeal, and all come with Leo’s stamp of approval — Judge Brett Kavanaugh, Judge Raymond Kethledge and Judge Amy Coney Barrett.