To regain power, Benjamin Netanyahu, the longest-serving Israeli prime minister, will most likely need the support of Itamar Ben-Gvir, a far-right leader with a history of extreme views.TEL AVIV — He was barred as a teenager from serving in the Israeli Army because he was considered too extremist. He admires a hard-line rabbi who wanted to strip Arab Israelis of their citizenship. Until recently, he hung a portrait in his home of Baruch Goldstein, who shot dead 29 Palestinians in a West Bank mosque in 1994.Itamar Ben-Gvir, a rising far-right lawmaker, has long occupied the fringes of Israeli politics and been widely vilified for his extreme views. But now, as Israel prepares for its fifth election since 2019, and with the polls predicting a deadlock, he is likely to become a major player in Benjamin Netanyahu’s bid to regain power in the vote on Nov. 1.At a recent election rally for Mr. Ben-Gvir in southern Tel Aviv, supporters of Mr. Netanyahu were cheering on a candidate they knew would be critical for him.“We are from the same side,” said Limor Inbar, 58, an activist from Mr. Netanyahu’s Likud party. “We share the same ideology.”Israeli voters face a choice between Mr. Netanyahu’s bloc of right-wing parties — including Mr. Ben-Gvir’s far-right alliance — and the governing coalition of right-wing, centrist and left-wing parties, led by Prime Minister Yair Lapid, that share little more than opposition to Mr. Netanyahu. Mr. Lapid’s alliance lost its parliamentary majority in the summer, a year after ousting Mr. Netanyahu, giving him another chance at power.A Ben-Gvir election poster last week in Jerusalem.Avishag Shaar-Yashuv for The New York TimesAt the last election, in 2021, Mr. Ben-Gvir’s alliance only scraped into Parliament. This time, polls suggest it will be the second biggest group in Mr. Netanyahu’s bloc, and the third largest in the country.While right-wing dominance of Israeli politics is not new, Mr. Ben-Gvir’s rise illustrates how Mr. Netanyahu’s camp within the Israeli right has become more extreme and religious.As his traditional allies abandoned him, Mr. Netanyahu — though secular himself — has been forced to forge a stronger bond with ultra-Orthodox Jewish parties. And though wary of appearing in public with them, he has become more reliant on ultranationalists like Mr. Ben-Gvir.Three decades ago, Likud, then a more traditional conservative party, shunned Mr. Ben-Gvir’s ideological forbear, Meir Kahane, for being too extreme. Today, Likud has moved further to the right, Mr. Ben-Gvir has cooled his support for Mr. Kahane, and Mr. Netanyahu has few other potential partners.If Mr. Ben-Gvir helps return Mr. Netanyahu to power, the government will be dependent on a lawmaker who hopes to upend Israel’s judicial system, grant legal immunity to Israeli soldiers who shoot at Palestinians, and deport rival lawmakers he accuses of terrorism.Less than two years after entering Parliament, “Ben-Gvir is the most important figure in the Israeli right wing after Netanyahu,” said Nadav Eyal, a leading Israeli political commentator.“We are from the same side,” said Limor Inbar, 58, left, an activist from Benjamin Netanyahu’s Likud party. “We share the same ideology.”Avishag Shaar-Yashuv for The New York Times“He is not only popular with right-wing voters,” Mr. Eyal said. “He’s getting out the votes of people who never voted before.”For more than a quarter-century, Mr. Ben-Gvir, 46, was relevant only on Israel’s far-right fringe. In 1995, he was filmed holding an emblem ripped from the car of Yitzhak Rabin, the Israeli prime minister who signed the Oslo peace accords.“Just as we got to this emblem, we’ll get to Rabin,” he said at the time. Mr. Rabin was later assassinated; Mr. Ben-Gvir had no connection to his murder.Mr. Ben-Gvir is an admirer of Meir Kahane, an Israeli American extremist assassinated in 1990 who wanted to strip Arab Israelis of their citizenship, segregate Israeli public space, and ban marriage between Jews and non-Jews.Mr. Ben-Gvir has often attended memorial events for Mr. Kahane, and has several convictions for incitement to racism and support for a terrorist group, as Mr. Kahane’s party is designated in Israel. A lawyer, Mr. Ben-Gvir has represented followers of Mr. Kahane and settlers accused of violence.Mr. Ben-Gvir in Israel’s Supreme Court this month.Avishag Shaar-Yashuv for The New York TimesToday, Mr. Ben-Gvir still calls Mr. Kahane “a hero,” but has distanced himself from Mr. Kahane’s most extreme policies.“I have no problem, of course, with the minorities here,” he said in a brief voice message, after declining a full interview. “But whoever is a terrorist, whoever commits terror — and anyone who wants jihad and to annihilate Jews, and not only that, also hurts Arabs — I have a problem with him.”In other interviews, he has said he has become more moderate.The portrait of Mr. Goldstein, who killed the Palestinians in 1994, no longer hangs in Mr. Ben-Gvir’s home. He regrets the episode involving Mr. Rabin’s car, he said in September. If he had actually “got to” Mr. Rabin himself, he would have only shouted at him, Mr. Ben-Gvir added.He has told his supporters to chant, “Death to terrorists,” instead of, “Death to Arabs.” He does not support expelling all Arabs, only those he calls terrorists.“This is a Jewish country,” he said in his voice message. But, he added, “I also want this country to be a safe country for all its citizens.”In May 2021, Mr. Ben-Gvir’s visit to a Palestinian area of East Jerusalem, Sheikh Jarrah, exacerbated unrest in the neighborhood that contributed to an 11-day war between Israel and militants in Gaza. This month, he returned to the neighborhood and encouraged the police to open fire on Palestinian stone-throwers.Avishag Shaar-Yashuv for The New York TimesThe sincerity of Mr. Ben-Gvir’s shift was placed in doubt in September by a senior member of his party, Jewish Power. In a leaked video, that party member, Almog Cohen, appeared to present his leader’s moderation as an election ploy.“Those who don’t use tricks, lose,” Mr. Cohen told a young supporter. Asked to elaborate by phone, Mr. Cohen declined to comment.But to many of his supporters, Mr. Ben-Gvir’s shift seems credible.He has moved “a long way” from Mr. Kahane’s ideas, said Sheffi Paz, a former leftist activist who now works with Jewish Power.Regardless, even the prospect of a reformed Mr. Ben-Gvir has drawn concern.In May 2021, his visits to a Palestinian area of East Jerusalem, Sheikh Jarrah, exacerbated unrest in the neighborhood that contributed to an 11-day war between Israel and militants in Gaza. This month, he returned to the neighborhood and encouraged the police to open fire on Palestinian stone-throwers.“Friends, they’re throwing rocks at us,” he said, pulling out his handgun. “Shoot them.”Some Israelis link his growing popularity to a gradual normalization of far-right thinking. The Israeli news media has granted Mr. Ben-Gvir more airtime this year than even some senior cabinet ministers, enhancing his profile.Supporters of Mr. Ben-Gvir this month in Tel Aviv.Avishag Shaar-Yashuv for The New York Times“The mainstream, average opinion in Israel has become closer to him,” said Ilan Rubin Fields, a documentary film director who interviewed Mr. Ben-Gvir in 2018. “I don’t think he’s that much more radical than the average person you’d stop in the street,” Mr. Fields added.Others attribute Mr. Ben-Gvir’s prominence to Mr. Netanyahu’s desperation.Mr. Netanyahu refused to leave office after being placed on trial for corruption in 2020, prompting right-wing allies to abandon him. That forced him to look for allies elsewhere.Since 2019, Mr. Netanyahu has helped broker alliances between far-right groups, including Mr. Ben-Gvir’s, that would have struggled to enter Parliament alone. His interventions helped legitimize Mr. Ben-Gvir, gave him a bigger platform and ultimately got him elected.The most recent intervention, in August, ensured another far-right party could benefit from Mr. Ben-Gvir’s now rocketing popularity.“Because of the threats Netanyahu feels for his very immediate and personal future, he is willing to lay his hand on Ben-Gvir and include him in his camp,” said Tomer Persico, a research fellow at the Shalom Hartman Institute, a research group in Jerusalem. “That changes the whole of the Israeli political map.”A Ben-Gvir rally last week in Tel Aviv.Avishag Shaar-Yashuv for The New York TimesMr. Ben-Gvir’s rise has also been propelled by young ultra-Orthodox voters who have grown disenchanted with traditional religious parties and right-wing secular Israelis who voted in the last election for Naftali Bennett.A former settler leader, Mr. Bennett was expected to help extend Mr. Netanyahu’s tenure. But he angered his base by forming a coalition with Mr. Lapid instead, as well as, for the first time in Israel history, a party from the country’s Arab minority.To his former supporters, the decision endangered the country’s Jewish identity and stifled the government’s ability to deal with Arab militants. It drove some of them to Mr. Ben-Gvir.“We have to save our Jewish state,” said Ms. Inbar, the activist.She stood behind Mr. Ben-Gvir at his rally, holding up a placard that suggested that only a right-wing government could block Arab influence on Israeli politics.“Yameen o Falasteen,” the sign said in Hebrew. “The Right — or Palestine.”Mr. Ben-Gvir entering the Supreme Court to discuss a petition he filed against the signature of the maritime border agreement with Lebanon.Avishag Shaar-Yashuv for The New York TimesGabby Sobelman More