Robert M. Morgenthau, the scion of a politically prominent family who became one of the country’s most powerful district attorneys and who revolutionized how the job is done while humbling rogue banks, crooked politicians, racketeers and rapacious corporate chiefs, died July 21 at a hospital in Manhattan. He was 99.

His son Robert P. Morgenthau confirmed the death but did not cite a specific cause.

From 1975 through 2009, Mr. Morgenthau served nine terms as New York County district attorney. Republicans, viewing him as invincible, gradually stopped fielding opponents.

Mr. Morgenthau became so closely identified with the office that the creators of the NBC series “Law and Order” used him as a model in the 1990s for their austere, sagacious district attorney, Adam Schiff, who was played by Steven Hill. In 2010, the American Bar Association Journal called Mr. Morgenthau “America’s D.A.”

His reputation attracted generations of bright young lawyers to what was sometimes called the “Morgenthau academy.” Eliot Spitzer and Andrew Cuomo, future New York governors, were among the alumni. “The Boss,” as he was called, was sometimes chided by outsiders for favoring offspring of the elite; John F. Kennedy Jr. was Exhibit A. Many of his assistant district attorneys had much more modest roots, including future Supreme Court Justice Sonia Sotomayor.

Mr. Morgenthau transformed his office into one of the most influential and hard-driving in the country through a combination of political savvy, an elbows-out demeanor and a refusal to let geography confine his range of targets.

He championed white-collar investigations, including money laundering at the Bank of Credit and Commerce International, in addition to prosecuting criminal cases involving “subway vigilante” Bernhard Goetz and the mother-son grifters and killers Sante and Kenny Kimes.

Mr. Morgenthau also pioneered the approach of going after gun sellers out of state — mainly in Virginia — whose wares showed up at New York City crime scenes.

One of the more sensational cases Mr. Morgenthau’s office handled was the 1990 rape of Trisha Meili, a white jogger in Central Park, ostensibly by a gang of black youths. She was so badly injured that she remembered little of the attack.

The assault heightened racial tension and triggered howls for justice. Detectives focused on several teenagers known to have been in the vicinity. Five ultimately were convicted and imprisoned. New evidence, including DNA indicators, surfaced years later, pointing to a different culprit. Over the objections of police and some of his own subordinates, Mr. Morgenthau had the convictions vacated in 2002.

“I think it was his finest hour,” Barry Scheck, co-founder of the Innocence Project, which uses DNA testing to reverse false convictions, told the ABA Journal in 2010. “Very few DAs would have done that. But he could, with his stature, guts and commitment to principle.”

Born into a wealthy German Jewish clan, Mr. Morgenthau was heir to a family that enjoyed influence in finance and Democratic politics for generations. His paternal grandfather, Henry, made a fortune in real estate and became President Woodrow Wilson’s ambassador to the Ottoman Empire. Mr. Morgenthau’s father, Henry Jr., was President Franklin D. Roosevelt’s treasury secretary for much of the Depression and World War II.

“We always spent New Year’s Eve at the White House and election night at Hyde Park,” Mr. Morgenthau told New York magazine, referring to the Roosevelt estate along the Hudson River in New York state.

As a young man, he helped first lady Eleanor Roosevelt serve hot dogs to King George VI and his wife, Queen Elizabeth, when the royals visited Hyde Park. In his teens, he was a sailing buddy of John F. Kennedy.

While working in corporate law, Mr. Morgenthau led the Kennedy presidential campaign’s Bronx organization in 1960. His reward was appointment as U.S. attorney for the Southern District of New York, a job he held for much of the decade. He created a securities fraud unit, reportedly the first in a U.S. attorney’s office.

One theme he repeated over decades: “If government is to be perceived as fair, it has to prosecute both drug dealers and white-collar criminals.”

Sometimes he seemed to go out of his way to pursue fellow Brahmins. In 1963, he obtained jail time for James M. Landis, who was found guilty of tax fraud; the former Harvard Law School dean was an adviser to Kennedy and his father, Joseph P. Kennedy Sr.

Later, as district attorney, Mr. Morgenthau’s fiefdom was ostensibly Manhattan. But he took an expansive view of the “impact jurisdiction” concept. If he thought offenses bore on Manhattan, he could chase offenders far afield.

Thus a Senate investigator, Jack Blum, arrived in 1989 with a dossier on the Bank of Credit and Commerce International, sired in the Middle East and chartered in Luxembourg.

Neither the Justice Department nor foreign regulators were pursuing information developed by a Senate subcommittee about BCCI’s real business — global money laundering. Furthermore, BCCI was thought to control, secretly and illegally, First American Bankshares, which had branches in New York.

“The boss called me in,” said John Moscow, then head of the fraud bureau. “He said, ‘There’s a dirty bank in New York. Let’s do something about it.’ ”

BCCI operated in 73 countries and wielded influence in many capitals. That included Washington, where Clark M. Clifford and Robert A. Altman — law partners and political insiders — had become executives of American Bankshares.

When the Morgenthau investigation approached the indictment stage, federal authorities and regulators abroad joined the hunt. Sixty prosecutions in several countries ensued.

BCCI imploded in 1991 under the pressure. It forfeited all assets in the United States — $550 million — and paid a fine of $10 million. American Bankshares, reduced to a shell, was bought out. A 1992 report by the Senate Foreign Relations Committee said: “Morgenthau not only broke the case on BCCI but indirectly brought about BCCI’s global closure.”

That wasn’t the finale. Mr. Morgenthau was accused of excessive zeal for obtaining fraud indictments against Clifford and Altman. A New York jury acquitted Altman. Federal and state criminal charges against Clifford — aging, ailing, famous as an adviser to presidents — were dropped. The two reached a settlement of $5 million with the Federal Reserve.

“I have no regrets,” Morgenthau said at the time. “This was a case that had to be tried.”

Big-bank bulldog

Robert Morris Morgenthau was born in New York on July 31, 1919. He graduated in 1937 from the private Deerfield Academy and in 1941 from Amherst College, both in Massachusetts.

During World War II, he served in the Navy and in 1944 survived the sinking of the destroyer USS Lansdale by German planes in the Mediterranean. His decorations included two awards of the Bronze Star.

After finishing Yale Law School in 1948, he rose in corporate law and politics.

Barely a year into his job as U.S. attorney, he was tapped by the Democrats to run against incumbent New York Gov. Nelson A. Rockefeller in 1962. Rockefeller seemed the strongest liberal Republican who might challenge President Kennedy’s reelection in 1964.

Mr. Morgenthau, who resigned as U.S. attorney, could not match Rockefeller’s campaign coffers and suffered an acute charisma deficit. Rockefeller trounced Mr. Morgenthau by 520,000 votes, and Kennedy reappointed him U.S. attorney.

After winning the race for New York County district attorney, Mr. Morgenthau instituted many structural changes. Among them was the creation of the Career Criminal program, concentrating resources on the 20 percent of the criminal population that, studies showed, commit 80 percent of serious offenses. The so-called 80/20 rule, a startling insight then, is now widely accepted.

Probes of big banks adorned the Morgenthau record. In 2006, he launched an inquiry into Credit Suisse allegedly using illicit means to help Iran access the U.S. financial system, in violation of U.S. sanctions.

Again, federal authorities followed his lead. In 2009, Credit Suisse agreed to a settlement of $536 million, divided evenly between New York and the U.S. Treasury. The Wall Street Journal observed at the time, “Mr. Morgenthau’s office has become a key front in the financial campaign against Iran.”

“One thing I learned about banking a long time ago,” he told the ABA Journal in 2010. “It’s all about deposits. Only the threat of prosecution keeps them honest.”

Mr. Morgenthau’s first wife, Martha Pattridge, died in 1972. He was a balding, wonkish establishmentarian when he met Lucinda Franks, 27 years his junior, in 1976.

She had won a Pulitzer Prize in 1971, with Thomas Powers, for their reporting on the Weathermen movement for United Press International, and she called herself an “unreconstructed radical.” He smoked cigars; she smoked pot. In her 2014 memoir, “Timeless: Love, Morgenthau and Me,” Franks described the romance as lust at first sight. And he cooked pancakes on their first morning-after.

They wed in 1977. In addition to wife, survivors include five children from his first marriage, Jenny Morgenthau of Manhattan, Anne Grand and Robert P. Morgenthau, both of the Bronx, Elinor Morgenthau of the Finger Lakes region of New York and Barbara Lee of San Francisco; two children from his second marriage, Joshua Morgenthau of Brooklyn and Amy Morgenthau of Manhattan; six grandchildren and three great-grandchildren.

In 2009, on the cusp of 90, Mr. Morgenthau announced he would take “early retirement.” He told an interviewer there was only one other job he coveted: the district attorney character played by Hill on “Law & Order.”

“I told him once when we met that I wanted to know when he was resigning because I wanted his job,” he said. “You know he got paid something like $25,000 an episode?”