JERUSALEM - At sunset in the Orthodox Jewish neighborhood of Har Nov, the ground-floor synagogue at the Yehaveh Da'at yeshiva hums with men murmuring prayers. An elderly bearded rabbi enters, and the sound becomes a chant. He's wearing a black turban, black-and-gold robe and rose-colored glasses. The room falls silent as he sits at the lectern and begins lecturing in conversational Hebrew to the young yeshiva boys seated or sprawled at the front. The older men sit in rapt attention.
Meet Ovadia Yosef, age 80, possibly the second-most powerful man in Israel though he holds no public office.
As spiritual leader of the Shas political movement, he controls the second-largest faction in Prime Minister Ehud Barak's ruling coalition.
Shas has triumphed in a bare-knuckled showdown with the prime minister that pushed Barak's most liberal allies out of the Cabinet and weakened government control over the movement's taxpayer-subsidized school system.
Now Israel and the United States are watching to see how Yosef tilts on crucial issues at stake in talks with the Palestinians. A nod in the wrong direction could send the peace process into a tailspin.
To Yosef's followers, he is "the genius of Israel, the minister of Torah, greatest Halachic ruler of the generation," as a poster announcing his sunset lecture series at the yeshiva describes him.
To his critics, he is a demagogue with little idea of democracy, capable of inciting his followers to violence against those who stand in his way.
Yosef's power base is in communities such as Har Nov, home to ultra-Orthodox of Sephardic descent who came to Israel from North Africa and the Middle East.
But his support reaches beyond the closed religious world to include many poor and lower-middle-class Sephardim who have felt discriminated against by the Ashkenazi elite from Europe who have long dominated Israeli institutions.
"He gives them pride," said Yoel Nir, an Israel Radio journalist who wrote a book about Shas political leader Arieh Deri. "He gives them pride as a scholar, and walking among prime ministers and generals, he shows them his strong hand."
Born in Baghdad in 1920, Yosef came to Palestine as a small boy with his parents. His father was a grocer and a cantor who sang at weddings.
Early on, young Yosef showed a prodigious bent for religious scholarship.
"He was known for a wonderful memory" and was able to quote chapter and verse from Talmudic teachings. Nir said. His personal library is said to number 30,000 volumes. He has written at least 20 books, most prominently an eight-volume work, "Yabia Omer."
His formidable knowledge is widely acknowledged. A Washington-based writer on Jewish intellectual trends, Yehuda Mirsky, went so far as to describe Yosef in the Jerusalem Report as "one of the greatest Jewish scholars of the 20th century." But there is debate about his depth as a thinker.
After becoming a judge in a religious court at a young age, Yosef took a senior rabbinical post in Cairo, Egypt. There, according to Mirsky, "he courageously insisted on preaching in Hebrew and refused to toe the government's anti-Israel line."
Returning to Israel in the 1950s, he rose in the rabbinical ranks to become chief Sephardic rabbi of Israel in 1972.
Drawing on a Sephardi tradition that is more lenient than that of the Ashkenazi ultra-Orthodox, he supported allowing nonspeaking deaf men to be counted in a minyan, the number of men required for a Jewish service, and broke with Ashkenazi rabbis in ruling that Ethiopian immigrants were fully Jewish.
"He put Sephardic tradition in the mainstream of Halachic [Jewish law] studies," said Menachem Friedman, an expert on the Orthodox at Bar-Ilan University.
Yosef was pushed out as chief rabbi in 1983 when the parliament, fed up with his Ashkenazi counterpart, passed a law limiting all chief rabbis to 10-year terms.
Yosef's political role emerged in the following decade in partnership with Deri, one of the early leaders of the Shas party. While formed by Sephardim disenchanted by their treatment in other religious parties, Shas at first was controlled by an Ashkenazi rabbi, Eliezer Schach.
Yosef didn't break Schach's hold until 1994, when he persuaded Deri to join Yitzhak Rabin's Labor-led coalition government.
Since then, Shas' strength has grown to where, in last year's election, it won 17 seats in the parliament, falling just behind the right-wing Likud party.
With its strength has come increasing skill at manipulating the levers of power and extorting money and favors from the government in exchange for support. Its political brinkmanship has outlasted Deri, who was convicted last year of taking bribes.
Since joining Barak's coalition last summer, Shas' new parliamentary leader, Eli Yishai, has bedeviled the prime minister and brought the government to the brink of collapse with repeated demands for more money and less regulation for Shas schools.
Critics say Shas' single-minded determination to expand religious instruction will come at the cost of academic subjects, leaving students poorly qualified to compete in a modern world.
A particular Shas target was Education Minister Yossi Sarid, from the secular and liberal Meretz party. Meretz recently quit the government to allow Barak to appease Shas, but not before Yosef let off a broadside against Sarid that was widely condemned as incitement and triggered an investigation by the attorney general.
In a speech in mid-March, Yosef denounced Sarid as Satan and compared him to Haman and Amalek, two ancient enemies of the Jews. "Just as he showed us in killing Haman and the vengeance done to Haman, so will vengeance be done to Sarid," Yosef said.
For many, the speech was a frightening reminder of the kind of right-wing threats that preceded the assassination of Yitzhak Rabin in 1975. Yosef later said he was not calling for physical violence. But it wasn't his first such outburst. Early last year, he attacked the Israeli Supreme Court as "wicked, stubborn and rebellious."
Not only Barak, but U.S. officials including peace envoy Dennis Ross and Ambassador Martin Indyk are prepared to overlook such behavior and troop to Yosef's second-floor home in a modest Har Nof apartment building in hopes that he will lead his followers to support peace agreements with the Palestinians and eventually with Syria.
Their hope is based on a speech Yosef gave in 1989 that shook the religious right in Israel. In it, Yosef declared that it was permissible for Israel to relinquish holy land for the sake of peace. He has since reaffirmed it.
But such an agreement would put Yosef in a tough dilemma, because many Shas supporters oppose trading land.
"No one knows how he will act or how many will follow. He said once he doesn't want to test it," Nir said.