The name the next pope chooses could provide the first clue about what his papacy will become.
For roughly 1,000 years, it has been traditional for a new pope to take a new name. And often, though not always, new popes have picked their names to honor a previous pope or to signal what kind of pope they want to be.
For example, Pope Julius II "chose his name not for a saint, not for a previous pope, but for Julius Caesar," said James Keating, a theologian at Providence University. "By that, he was signaling his attempt to be a military pope."
If the next pope chooses to name himself John Paul III, it would signal a continuation of John Paul II's ideals, Vatican watchers say.
A different name may indicate a new direction.
"If the pope chooses Leo, he can say that he is going to emphasize the social mission of the church," Keating said, "because the last Pope Leo, Leo XIII, was a great critic of capitalism."
Other recent popes' legacies might attach meanings to their names -- with John perhaps suggesting a reformer and Pius suggesting a traditionalist.
Sometimes, as with Pius, a pope's name also can reflect a desired virtue. There have been 13 Innocents and 12 Piuses.
Other common pope names have been John, Gregory, Benedict, Clement and Leo. All have been used at least a dozen times.
Occasionally, popes have named themselves after relatives or mentors who were not popes.
The tradition of popes adopting new names dates back to 533 A.D., when a humble priest named Mercury became pope.
"He thought, 'Well, I can't be Mercury I — that is a name of a pagan god — and so he changed his name to John II,' " said Gerald O'Collins of the Pontifical Gregorian University. "So he started it. It hadn't happened before."
There were popes after John II who kept their own names, but around 1000 A.D., it became typical for popes to pick a new one.
Ever since, popes' real names have been largely forgotten. How many average Catholics remember the name Eugenio Pacelli, who became Pius XII in 1939, or Angelo Roncalli, who became John XXIII in 1958?
Twenty-seven years ago, a relatively unknown Polish cardinal entered the papal conclave as Karol Wojtyla and emerged two days later as Pope John Paul II, choosing to name himself after his predecessor, John Paul I -- who, in turn, combined the names of the two preceding popes to become the first pope with a double name.
Some pope names are unlikely to be used again. The name Peter long has been considered off limits in deference to the apostle who became the first pope. In the distant past, at least two men named Peter avoided using that name upon becoming pope.
Then there are long-ago pope names that might sound odd to modern ears -- such as the fifth century's Pope Hilarious.
"One name that is quite out," O'Collins said, chuckling, "is, there was a Sixtus V, and you couldn't have Sixtus VI."
The bookmakers already are picking their favorite pope names. On one Internet gambling site, Benedict is the top choice, at 3-1 odds. And perhaps contrary to O'Collins' thinking, Sixtus VI is listed, with 66-1 odds.
Then again, the new pope could choose a name never picked before, perhaps after an apostle like Matthew, or a name from his own country, such as an Indian or Nigerian name.
ABC News reporter Bob Woodruff and producer Stephanie Gosk originally reported this story April 17, 2005, on "World News Tonight."