Chairman and CEO of the Las Vegas Sands casino Sheldon Adelson (center), a donor to Republican presidential nominee Mitt Romney, speaks with other attendees at the end of the first presidential debate Oct. 3 in Denver. (JASON REED/REUTERS)

When casino magnate Sheldon Adelson switched his support from Newt Gingrich to Mitt Romney during the spring primaries, the billionaire and the candidate were eager to shed their skepticism of each other. If Adelson was going to give a political campaign more money than anyone ever had, he wanted to be certain Romney would join him in steadfast support of Israel. And Romney, according to friends of both, sought assurance that Adelson wouldn’t embarrass him.

Since then, Adelson has joined Romney during the candidate’s visit to Israel this summer, attended presidential debates and gotten together with Romney so often that their wives have become friends, according to confidants of the two men.

Although Adelson, 79, has said he will give $100 million to help Romney and quash President Obama’s “socialist-style” approach to the economy, he remains skeptical, believing that politicians don’t deliver on promises and can’t be trusted.

“Many people who give very significant donations to political campaigns come to me afterwards very frustrated that they don’t get what they wanted once the person is elected,” says Morton Klein, president of the Zionist Organization of America, which Adelson has supported for years. “Sheldon doesn’t expect people to change. He’s very realistic about politics.”

Adelson — whose gambling operations span the globe from Las Vegas to casinos open or planned in Macau, Singapore and Spain — tells friends he finds the way U.S. elections are funded to be abhorrent, putting too much power in the hands of a wealthy few. So as one of those wealthy few, why would he pour more money into a campaign than 65 average Americans will earn in their combined lifetimes?

Adelson would not agree to an interview unless he could screen all questions in advance, a condition The Washington Post declined to meet. But more than 20 friends, critics, colleagues and beneficiaries portray a man with several motives for his massive donations to political, religious and medical causes.

He’s a scrappy fighter who defends what is his, a self-made man who held more than 50 jobs before striking gold with his Venetian casino on the Vegas Strip, and he has developed a powerful aversion to taxes and unions. He is the 12th-richest person in the nation, according to Forbes magazine, with a fortune valued at $21 billion. ­Under Obama, Adelson has achieved a larger increase in his wealth than anyone else in the country. In the past two decades, he has also undergone a political conversion, from a Massachusetts Democrat who considered Republicans to be the establishment that resisted newcomers like him, to a Nevada Republican who believes that his former party coddles the idle and has fallen captive to identity politics.

Adelson is driven by the idea of Israel as a muscular riposte to the Holocaust. Based on his experience as a Jewish kid who would get insulted and roughed up in a tough Boston neighborhood, Adelson believes Jewish Americans should back an Israel that puts security first and resists compromise with Arabs who do not accept its existence.

“Israel is at the core of everything he does,” says Fred Zeidman, a friend of Adelson, fellow Romney backer and former chairman of the U.S. Holocaust Memorial Museum.

Adelson is something of a paradox. Jewish friends and foes alike call him a “shtarker” — a Yiddish term for a tough guy — yet his pattern of giving supports both his own business interests and more selfless pursuits, such as the more than $100 million he has given to Birthright Israel, a program that sends young American Jews on all-expenses-paid trips to the Jewish state.

His political giving backs his belief in an elbows-out capitalism in which entrepreneurs fight for profits and markets with the least possible regulation, but the vast sums he has given to medical science ask researchers to shelve their competitive instincts for the social good.

Whatever field he toils in, Adelson is “in­cred­ibly stick-to-itive,” says Michael Leven, president of Adelson’s Las Vegas Sands Corp. “He stands up for what he believes in. That’s why lawsuits happen.”

Adelson has been involved in legal conflicts with business competitors, unions, even his children — in one 10-year period, he was involved in more than 150 suits in Clark County alone, which includes Las Vegas.

In a suit in which his sons alleged that Adelson defrauded them by pressing them to sell stock for less than its fair value, a Massachusetts judge wrote in 2001 that Adelson was “a harsh, demanding, unfeeling, successful businessman” who was “perhaps lacking paternal kindness and, indeed, cordiality generally.” But the judge ruled for Adelson, saying he had neither misled nor cheated his children.

He does not shy from spending on himself and his wife, Miriam, an Israeli physician who focuses on treating drug addicts. He flies in his own Boeing 747, is driven in a Maybach and has expansive homes in Malibu and Las Vegas. He moves around with burly bodyguards who defend him against enemies, and against those asking undesirable questions.

Childhood friend Irwin Chafetz says that when he worked with him, he sometimes backed away from confronting Adelson, who even friends describe as bullheaded and aggressive. “A lot of times, people don’t want to aggravate him, so they just stand aside and let him do what he’s going to do,” Chafetz says. “In the end, all of us who have enjoyed financial success because of him say we are where we are because he is the way he is.”

Yet Adelson knows how he can come off. Leven tells of meeting in Las Vegas with officials from Vietnam about a possible business location there. “Sheldon didn’t like the location, so he had me meet with them because I would be more tactful,” Leven says. “He would tell them, ‘Your location stinks,’ whereas I talked to them and, next thing you know, I’m going on a helicopter ride to the site next time I’m in Vietnam.”

But Adelson also makes his jets available to employees who need medical care. He bails out childhood friends who have fallen on hard times. Every year, he flies dozens of battle-torn veterans on an all-expenses-paid trip to Vegas.

Adelson has no business degree — indeed, no degree of any kind. He knew little about computers or casinos before entering the fields that would make him rich. He says his success stems from his determination “to challenge and change the status quo.”

Critics say his overriding goal is to solidify control of markets in which he does business.

Friends and foes say Adelson gets what he wants by relentlessly protecting his turf, spending liberally on his product and making himself valuable to those who can help him succeed.

“He’s been a fighter all his life,” Leven says. “He’s physically short in stature and he never graduated from college, so he has to be more tenacious. It’s an effort to get ahead.”

Childhood in Boston

As World War II raged across the ocean, in a neighborhood of south Boston that was home to more Jews than any American city outside New York, kids like Sheldon Adelson learned that being a Jew in America both put a target on their backs and gave them a blessed refuge.

Like other Jewish teens in Dorchester, young Sheldon was occasionally beaten up by Irish kids full of anti-Semitic vinegar. Yet he knew that millions of other Jews faced vastly worse enemies in Europe.

Other Jewish boys found refuge in street games such as stickball and halfball, but Sheldon was never interested in sports, friends say. “He was interested in making money,” Chafetz says. Before he got to high school, Adelson bought the right to sell newspapers on a busy street corner.

Adelson sold windshield cleaners, stocked vending machines and, then, as a young man, scored on a travel agency he launched with old buddies. The profits allowed him to move to a more upscale area, into a house that boasted its own bowling alley.

These days, Adelson calls the place he came from “the slums,” and he has donated more than $50 million to support Jewish schools in the Las Vegas and Boston areas. Add his gifts to Birthright and $50 million given to Israel’s Yad Vashem (making the Adelsons that Holocaust museum’s largest donor), and Adelson’s support for Jewish causes vastly outstrips his political donations.

Adelson’s passion for Israel does not stem from religious devotion; he is not a regular at synagogue, does not speak much Hebrew, and is neither kosher nor Sabbath-observant, says Klein, who is both.

When Adelson first visited the Holy Land, he wore his father’s shoes as he stepped off the plane so something of his father’s would be the first to touch the ground.

Like Israeli Prime Minister Benjamin Netanyahu, whom he visits regularly, Adelson believes the Jewish state’s neighbors have proved unwilling to accept its existence.

To promote his view, Adelson five years ago launched a free tabloid, Israel Today, that has become the No. 1 newspaper in Israel and a loyal booster of Netanyahu, leading critics to charge that a foreign investor is having undue influence on domestic affairs.

Adelson’s attachment to Israel dates back decades, so few friends were surprised when, after his divorce, “he asked friends to fix him up only with Israelis,” Klein recalls. Adelson was introduced to Miriam Ochsorn, now 66. They married in 1991.

Adelson’s passion for Israel did not develop into Republican activism until the past two decades. Well into adulthood, he was a Democrat, making large donations to the party until 1996. The next year, he switched to the GOP.

“As Jews in Boston, no one voted Republican, because the Republicans were the establishment,” Leven says. “But Sheldon saw the Democrats becoming less passionate about Israel.”

Friends say two shifts in Adelson’s thinking led to his party switch. On Israel, “he saw the left as more compromising, and Sheldon is not a great compromiser,” Chafetz says.

And Adelson’s opposition to unions alienated him from Democrats.

“What makes him anti-union is not the money,” Chafetz says. “It’s the union rules. He changed philosophically. He doesn’t want to be told he has to have four people do the job if two people can do it. Sheldon is all about accomplishment. It rules his life.”

Union fight in Nevada

When Adelson took on Nevada’s largest union, the Culinary Workers Union, labor groups portrayed him as a bully intent on making money on the backs of workers.

The result was a battle royal. Starting in the 1990s, Adelson and the union fought for years over whether the union could demonstrate on sidewalks outside his hotel. (The workers won.)

Adelson’s $1.5 billion Venetian remains the only major casino on the Strip that is not unionized. The culinary union rejects Adelson’s claim that he provides his 6,300 workers with better pay and benefits than they would get under union contracts.

“He’s refused to speak to us,” says D. Taylor, secretary-treasurer of the union local. “This is not at all about money — it’s about power. Look, there are a lot of people who grew up poor. That’s not an excuse. The workers know they are at the mercy of the boss. This is someone who will come after you.”

Adelson says that when he believes he has been wronged, he will take action. “If people do something he considers underhanded,” Chafetz says, “he’s not going to let them get away with it.”

Adelson sued the Las Vegas convention authority over its expansion plans. He fought his sons for seven years. And this summer, he sued the National Jewish Democratic Council for $60 million after it posted an article saying he “personally approved of prostitution in his Macau casinos.”

The lawsuit came a week after the Democratic Congressional Campaign Committee apologized to Adelson for making the same allegation on its site. The original statement came from a lawsuit in which one of his former executives, Steve Jacobs, alleges that the billionaire condoned prostitution at his Macau casino, which Adelson vehemently denies.

Jacobs’s allegations are now the basis of investigations by the Justice Department and the Securities and Exchange Commission into whether Adelson’s company violated federal law banning bribery in foreign countries, according to federal sources, who said the probe is not expected to be completed before the November elections.

Adelson has been known to cut off those who disagree with his worldview. In 2007, when the American Israel Public Affairs Committee, which Adelson had supported financially, decided to support increased aid to the Palestinian Authority, Adelson halted his gifts to AIPAC.

But Adelson has remained supportive of the U.S. Holocaust Memorial Museum despite his view, according to three friends, that it is run by liberals and its programming leans left.

Aiding medical research

In 2004, Adelson developed a neurological problem that made it difficult for him to walk. He went from specialist to specialist. There was no clear diagnosis, no certain treatment.

He approached Bruce Dobkin, a neurologist at UCLA. After learning about the cumbersome ways in which medical research is funded and conducted, Adelson decided to launch an experiment. He set up a fund and asked Dobkin to recruit researchers who would collaborate to get results faster. The approach was a far cry from Adelson’s individualistic style in politics and business.

“In the political arena, he doesn’t want to pay any more taxes than he has to, and he hates unions, and he wants to make sure Israel survives,” Dobkin says. “He has no illusions that politicians will solve problems. He doesn’t ask them to be collaborative.”

But on social issues, Dobkin says, “the Adelsons are much more empathetic and liberal, in a sense, than people think.”

Part of that softer side stems from Adelson’s anguish over his two sons from his first marriage, both of whom struggled with drugs. Mitchell died of an overdose in 2005; Gary says he does not want to talk about his father, because they are rekindling ties after years of friction.

Adelson announced that he would spend “billions” on medical research. But it was not clear that the collaboration model would work. At a meeting with Adelson, a researcher from Harvard said he loved the idea but asked, “Who’s going to get credit?”

“I thought that was the death knell,” Dobkin recalls, “but then Sheldon perks up and says: ‘How many papers did Jonas Salk write? . . . Do you want to be remembered as the guy who wrote 200 or 300 papers or the guy who actually found a treatment that helps people?’ ”

The Harvard guy signed up. In the first years, Adelson researchers published hundreds of articles and shared results openly. Then came the financial collapse of 2008, drying up funding.

Leven says his boss remains committed to research. He acknowledges that the Adelson who plays political hardball may look very different from the philanthropist who preaches the gospel of collective research. But in the end, it’s all about getting what you want.

“In business, he doesn’t need cooperation from [casino magnate] Steve Wynn or MGM,” Leven says. “But in medicine, he found he could get a better result with a cooperative approach. He’s just being pragmatic. Sheldon is not a complex person. What you see is what you get.”