Joseph H. Flom, a lawyer whose expertise and ruthlessness in corporate mergers and acquisitions reshaped America's business landscape during the 1980s and helped turn his tiny New York firm into one of the nation's largest law practices, died Feb. 23 at a hospital in New York.

He was 87 and had a pulmonary embolism, said his wife, Judi Flom.

Mr. Flom was widely acknowledged as a master architect of hostile takeovers, in which a raider purchases a target company without consent.

Such unwanted advances by corporate suitors had long been scorned as dirty business by white-shoe law firms. To Mr. Flom - who grew up poor in Brooklyn, N.Y., and talked his way into Harvard Law School without earning an undergraduate degree - high-stakes takeovers were a path to power and profitability.

He and his firm - which became Skadden, Arps, Slate, Meagher and Flom - were involved in nearly every major merger and acquisition fight of the 1970s and 1980s, including U.S. Steel's multibillion-dollar takeover of Marathon Oil, Chevron's purchase of Gulf Oil and RJR Holdings' purchase of Nabisco.

More recently, Mr. Flom represented Anheuser-Busch in 2008 when it was purchased by the Belgian brewer InBev in a $52 billion deal.

He was best known for mapping strategies on behalf of buyers, often engineering costly and risky lightning raids in which his clients attempted to take over companies by offering more than market rate for shareholders' stock.

But Mr. Flom was so feared as an adversary that he was frequently paid handsome retainer fees by companies nervous about becoming takeover targets.

This was a practice known in the business, according to a 1994 book about Skadden, Arps by journalist Lincoln Caplan, as "sterilizing Joe" - as long as Mr. Flom worked for you, he couldn't come after you.

"I have no preferences for being on one side or the other," Mr. Flom told the Times of London in 1988. "The only thing I cannot stand is not being on either side."

Whether on offense or defense, Mr. Flom relished his reputation as a street fighter willing to go to any length to win. Caplan noted the lawyer's habit of jabbing a cigar "close to the face of someone he was talking to, without apology."

When a Flom client, the Mead paper company, was threatened with takeover in 1978, he launched a private investigation into wrongdoings by the raider, Occidental Petroleum, and its chief executive, business tycoon Armand Hammer.

Mr. Flom's investigators alleged that an Occidental subsidiary had caused environmental problems at Love Canal near Niagara Falls, N.Y. They also accused Hammer of personal ethical lapses, such as offering handsome payments to Soviet officials in exchange for art-collecting help.

Hammer dropped the takeover, saying that no "acquisition was worth this battery of problems."

The Occidental executive later hired Mr. Flom to represent his company.

"It is a great comfort to have Joe on your side," Hammer wrote in his biography, "and a sore distress to have him against you."

Joseph Harold Flom was born in Baltimore on Dec. 20, 1923, to Jewish immigrants from Russia.

At age 3, he moved with his family to Brooklyn, where his father worked as a part-time union organizer and his mother supported the family by doing applique work from home. The family moved frequently, taking advantage of landlords' offers of a few months' free rent and then departing for the next apartment.

Mr. Flom attended City College of New York until joining the Army during World War II. After the war, he followed his application to Harvard Law School with a letter to admissions officials detailing his strengths. He got in.

He said he was motivated by hunger to study law, which he expected would lead to politics and a life of relative privilege. "When you don't have enough to eat," he told a reporter in 2008, "you never forget that."

Upon graduation in 1948, he said, his Jewish heritage and admitted lack of social graces blocked him from jobs with prestigious law firms.

He landed his first position as the lone associate working under three young partners - Marshall Skadden, Leslie Arps and John Slate - who also had been turned down by established firms. "We've got to show the bastards that you don't have to be born into it," Mr. Flom often told his colleagues.

Rather than polishing his manner, he used his coarse and scrappy demeanor to build a reputation for clever, determined aggression, especially in corporate proxy fights, when shareholders mount an attempt to influence management decisions.

He became a named partner in 1960, and over the next several decades was a driving force behind the rise of Skadden, Arps into a sprawling general practice with a specialty in mergers and acquisitions.

By the late 1980s, he reportedly earned at least $500 per hour and the firm made an estimated $10 million a week. It now employs 2,000 lawyers in two dozen offices around the world and brings in more than $2 billion in revenue each year.

The watershed moment for Mr. Flom and his firm came in 1974, when he advised the investment bank Morgan Stanley and its client, the International Nickel Co. of Canada, widely known as Inco, in a hostile takeover of a Philadelphia battery manufacturer called ESB.

That effort helped legitimize takeovers, which soon came to define and drive Wall Street.

"It was precedent-setting," wrote Fairleigh Dickinson University economics professor Patrick Gaughan in his 1996 book, "Mergers, Acquisitions and Corporate Restructurings." "Firms and their chief executives who had inclined to be raiders but had been inhibited by public censure from the business community now became unrestrained."

Mr. Flom was a past chairman of the Woodrow Wilson International Center for Scholars in Washington. He donated generously to Democratic candidates and gave millions of dollars to philanthropic causes, particularly those with an education focus.

He established a fellowship program for recent law school graduates who aim to work in public interest law.

He also played a key role in establishing a program to help poor and minority students at the City College of New York prepare for admission to top law schools.

His first wife, Claire Cohen Flom, died in 2007. He married Judi Sorensen in 2008.

Besides his wife, survivors include two sons from his first marriage, Peter Flom and Jason Flom, both of New York; a stepdaughter, Nancy Laing of New York; six grandchildren; and two great-grandchildren.

Mr. Flom had a legendary capacity for work - during a six-week family vacation in Spain, he flew back to the United States five times to advise clients.

"Hold my calls," he'd tell his secretary during busy moments. "Unless it's new business!"