Reuters; Hulton Archive/Getty Images

Left, Pope Benedict XVI blesses the faithful for the last time. Right, his namesake Pope Benedict XV, circa 1915.

The first clue about what kind of leader the next pope will be — liberal or conservative, reformer or by-the-book — will come only minutes after the smoke clears at the Sistine Chapel.

From a balcony at St. Peter’s Basilica, the world will learn not just who has been elected but what he chooses to call himself, a decision steeped in centuries of church history — and a good indicator of the new pope’s vision and inspiration.

Until the sixth century, popes went by their given names. There was a Pope Sylvester, a Pope Julius and a Pope Victor. Then, in 533, a priest named Mercurius was elected to lead the church and decided that a pope named after a pagan god  — "Mercury" — just wouldn’t do.

He chose to go by John II. Since then, most popes have abandoned their birth names and adopted tributes to saints, popes and even relatives who have gone before.

“You’re trying to pick up some of the glow of your predecessor,” said the Rev. Thomas Reese, Vatican analyst for the National Catholic Reporter.

It is a solemn decision. Newly-elected popes are asked only two questions by the senior cardinal inside the chapel. The first is whether he wants the job. The second: “By which name do you wish to be called?”

When Cardinal Joseph Ratzinger was elected pope, in 2005, he chose Benedict XVI as a tribute to two men. One was the previous Pope Benedict, who guided the church through World War I. But Benedict XVI said that he also meant the choice as homage to St. Benedict, an intellectual like Ratzinger and one of the patron saints of Europe, for his “powerful call to the irrefutable Christian roots of European culture and civilization.”

In particular, Benedict XVI prayed to his saintly namesake to help Catholics keep Christ at the center of their lives.

“Benedict saw Europe as the key problem and the place where we really needed to focus,” Reese said.

But the choice is not always a nod to papal history. The reformer Pope John XXIII, elected in 1958, said he picked the name it part because it was the name of the small parish church where he was baptized. John is by far the most popular name for a pope to choose, making it  difficult to predict what a John XXIV would be signaling by taking the name.

In 1978, Cardinal Albino Luciani declared himself Pope John Paul I, the first pope to choose a double name — and the first to declare himself “the First.”

He said that he meant the name as a tribute to his two immediate predecessors, John XXIII and Paul VI. They had led the church through the Second Vatican Council, which modernized the church’s relationships with the rest of the world and other branches of Christianity.

When John Paul I died just 33 days later, he was remembered so adoringly that Reese recalls making a bet with a colleague that the next pope would take the same double name.

“He just caught everybody’s imagination,” Reese said. “This smiling pope. It was just a whole month of very positive response to him.”

He won the bet, and Pope John Paul II led the church for the next 27 years.

This time around, only one bet would be a sure loser. No pope has chosen to be called Peter II. There’s no rule against it, but it is seen as poor form — an honor reserved for the first pope.

Church analysts say there are several names to watch for as hints to the new papacy.

The choice of Leo XIV could be a call for social justice, said Matthew Bunson, senior correspondent for the Catholic publishing nonprofit Our Sunday Visitor. Leo XIII, who served at the turn of the 20th century, and sought to help the world understand the dignity of workers.

Choosing Pius XIII, on the other hand, would be a more conservative choice, and a “statement of determination to defend the teachings of the faith,” Bunson said. Pius V led in opposition to the Protestant Reformation, and Pius VI and VII both died prisoners.

John Paul III, even if only as a tribute to the beloved, globetrotting John Paul II, might be seen by the world as a repudiation of Benedict, Reese said.

Of course, the new pope could always choose to be called Benedict XVII — certainly a possibility because Benedict XVI appointed most of the cardinals who will choose his successor. But such a selection might disappoint Catholics who are hoping for a reformer after a papacy marked by a sexual abuse scandal, other missteps and shrinking membership in the United States and Europe.

Beyond that, it’s anyone’s guess. The new pope could choose to make his mark and choose a name never used before. Reese said he has always wondered why no one has adopted the name Pope Joseph.

Or he could set 1.2 billion Catholics around the world scratching their heads.

“The new guy,” Reese said, “could be John Paul Benedict I.”

Slideshow: Electing a pope

Andrew Medichini / AP

Cardinals from around the world gather in the Vatican to elect the next leader of the Roman Catholic Church.

Launch slideshow

Related: 

Full coverage of the papal abdication from NBC News

This story was originally published on Tue Mar 12, 2013 6:29 PM EDT