One of the most consequential Catholics of modern times is also one of the least heralded and most enigmatic.

His name is William P. “Bill” Clark, known as “The Judge,” because of his decade of service on the bench, including the California Supreme Court. Those appointments followed his service as chief of staff to Gov. Ronald Reagan in the 1960s and preceded his service as President Reagan’s deputy secretary of state, national security adviser and secretary of the interior in the 1980s — the positions through which Bill Clark changed history as Reagan’s most trusted aide and adviser.

The Clark story is a moving saga of what was and what might have been, a remarkable trail of footprints in the sand — a fitting image, given that every one of us acknowledges the footprints but are unable to see the figure who left them.

That path for Bill Clark started to come into focus in 1950 when he left an Augustinian novitiate in New York’s Hudson Valley, putting aside the priesthood for a career as a lawyer, rancher and a litany of unforeseen public service that he and Reagan would in retrospect refer to as part of “the DP “— “the Divine Plan” that Providence had in store for them.

To fully chronicle “the DP” requires a book, not an article — something I know well as Clark’s biographer. Most significant, however, were two examples from 25 years ago.

First, what might have been:

In June 1981, Bill Clark was serving Ronald Reagan at the State Department when U.S. Supreme Court Justice Potter Stewart announced he was resigning. Reagan called “The Judge” into his office to ask him if he would like to be considered for the position.

Before considering Clark’s answer, pause for a moment to consider the offer:

Bill Clark had been a rancher’s son from rural California, a family that lived off the land during the Great Depression. His beginnings could not have been more humble.

He learned about the likes of Fulton Sheen not from TV — like most people — but from books, since his family could not afford a television. He managed to become a lawyer without ever earning a law degree, taking just enough schooling (that which he could afford) to learn enough to pass the bar exam the second time around.

He became a lawyer and a judge, and the ultimate honor would be to serve on the U.S. Supreme Court. Bill Clark, however, declined the president’s generous offer.

The quintessential citizen/public official, the lawmaker or policymaker who puts down his plow for a few years to serve his country, and then returns to the plow, Clark had come to Washington to serve his president and his country, to accomplish some goals and then to return to his family and his ranch. This was selfless service, as America’s Founding Fathers envisioned public life.

Clark did not go to Washington to pad his resume, become famous and die on the Supreme Court. Ronald Reagan knew that, which is one of the reasons he so liked and trusted Clark.

“That’s what I thought you would say, Bill,” said President Reagan with a grin, as he crossed Clark’s name off a short list of potential replacements for Stewart.

Instead, the position went to Sandra Day O’Connor. And that is the story of what might have been: If Clark had taken that Supreme Court seat in 1981, he would not have voted the way that O’Connor did on pivotal abortion cases like Casey v. Planned Parenthood (1992). If Clark had taken that job — which I have no doubt was his for the taking — Roe v. Wade would have been reversed.

That was no doubt a major regret of Clark’s.

But the DP had something else in store. Rather than wage the culture war, Bill Clark would wage the Cold War.

Six months later, he was tapped by Reagan to run the National Security Council, the nation’s premier body for implementing national security and foreign policy. It was in that capacity that Clark, as Reagan’s closest and most influential adviser, became — by all accounts — the most powerful man in Washington (next to the president himself) and, by extension, one of the most powerful men in the world.

It was there, too, from that position of remarkable power and influence — to which he never aspired — that Clark from January 1982 through October 1983, often working in consultation with only Reagan and no one else in the room, laid the foundation to undermine the Soviet Union and win the Cold War through a series of extraordinary and only recently declassified National Security Decision Directives.

In addition to that work, Clark did a great deal for and with Reagan to stop the Soviet Union, from shepherding the president’s announcement of the Strategic Defense Initiative, to being the White House figure who worked with the Catholic bishops on controversial issues like the MX missile, to serving as the principal liaison between the Reagan administration and Pope John Paul II’s Vatican.

It was Clark who helped set up the June 1982 meeting at the Vatican when Pope John Paul II and the president confided in one another that they believed that God had spared their lives from assassination attempts the previous year for the purpose of undermining atheistic Soviet communism.

From there, Clark (along with another instrumental Catholic, CIA director Bill Casey) met weekly, sometimes daily during moments of crisis, with Cardinal Pio Laghi, the apostolic delegate to the United States, at Cardinal Laghi’s residence or other undisclosed locations, at times via a back door at the White House.

By the time Clark left the National Security Council in late 1983, the pieces were in place for the Soviet downfall.

Clark was arguably the most important American Catholic in the collapse of communism and the end of the Cold War, and, in that respect, the second most important Catholic worldwide, behind only Pope John Paul II.

Yet most Catholics have never heard of the man. And why not?

Because of Clark’s genuine humility. He wouldn’t sell his story or write memoirs even when everyone from Reagan’s most liberal biographers to most conservative cabinet secretaries urged him to do so.

Only now, near the end of his life, did he consent to a biographer’s request to tell his story. And, only then, the biographer prevailed by appealing to Clark’s sense of duty to Reagan, to America and to history — to setting straight certain key facts that only he knew. And, still, he remains highly uncomfortable by the attention.

Today, the 76-year-old Clark spends his final days at his ranch in Paso Robles, Calif., still surrounded by the works of the great Catholic minds that inspired him for decades, from Aquinas to the latest editions of Sheen’s Peace of Soul that rest on the coffee table in front of him.

There he also pursues his final calling: He has built a chapel on his ranch, which holds regular Mass and which plays host to some of the finest minds in modern Catholicism: Franciscan Father Benedict Groeschel, founder of Priests for Life Father Frank Pavone, Jesuit Father Joseph Fessio, Cardinal Christoph Schönborn.

It is there, near the Blessed Sacrament on the inside, and, on the outside, a small Italian fountain featuring a plaque inscribed with the Peace Prayer of St. Francis — which Bill Clark and Ronald Reagan prayed together — that Clark spends his final years, struggling with the onset of Parkinson’s disease and even the occasional battle with what John of the Cross called “the dark night of the soul.”

Of the Parkinson’s, he says, “God gave Parkinson’s to such saints as John Paul II and my father, and now he has gotten around to the sinners, such as myself.”

There, too, Clark also deals with, to borrow from St. Augustine, a God-shaped vacuum, a yearning for the priesthood that remains since those days at the Augustinian novitiate in New York.

It seems unlikely that a man of so many accomplishments can still feel any longing, but, then again, Bill Clark’s story has always been unlikely — and underappreciated.

Paul Kengor, professor of political science at Grove City College, is author of The Judge: William P. Clark, Ronald Reagan’s Top Hand (Ignatius Press, 2007).