Peter J. Zwack, a Hungarian-born liquor magnate who helped safeguard the secret formula for his family’s prized Unicum digestif during years of Nazi and Soviet occupation and served a tempestuous stint in Washington as the ambassador from Hungary in the early 1990s, died Aug. 4 in Venturina, Italy.

He was 85 and died, apparently of overexertion, while swimming at a hot springs spa near his home in the Tuscan town of Bolgheri, said his son Peter B. Zwack.

Mr. Zwack cut an unusual figure in the diplomatic corps when he arrived in Washington in 1990. The Washington Post once described him as “one of the most colorful among the ambassadors in Washington” and later, after an unbecoming departure, “one of the most controversial.”

A celebrity in his native country, Mr. Zwack managed in the late 1980s to reclaim control of his family’s famed Zwack distillery — the producer of Unicum, an 84 proof bombshell sometimes called the Hungarian national shot — after four decades of communist government ownership.

Western news media hailed him at the time as apparently the first businessman in the nationalized economies of Eastern Europe to achieve such a feat. There were calls in Hungary for him to run for president.

Peter J. Zwack, a Hungarian-born liquor magnate who later served as ambassador to the United States, died Aug. 4. (Bill Snead/THE WASHINGTON POST)

Beyond those distinctions, Mr. Zwack was a naturalized U.S. citizen and therefore an unlikely candidate for a foreign ambassadorship. He and his family had fled to the United States in 1948, after the government nationalized the distillery. They left behind a bogus recipe for Unicum, a concoction made from 40 herbs and roots that was created, according to family lore, in the late 1700s by a Zwack ancestor.

During communist control in Hungary, the government-owned Zwack distillery produced a version of Unicum that was not quite right. Mr. Zwack’s father had tucked the bona fide formula in his back pocket when he escaped from Budapest to Vienna, hidden under an oil drum on a Soviet truck. Mr. Zwack later helped store the recipe — split into four parts for added security, according to news accounts — in safe-deposit boxes at four New York banks.

He had arrived at Ellis Island stripped of his considerable family wealth. He sold vacuum cleaners before finding work, first in New York and later in Chicago, in the wine-and-spirits import-export trade.

In 1971, he moved to Italy, where he joined a relative who had been producing small quantities of Unicum — the real thing — for connoisseurs around the world who did not buy from the communist-run distillery.

Then, in 1988, the reform-minded “goulash communists” invited Mr. Zwack to return to Hungary. He agreed and, over time, reclaimed control of the distillery. Today it is known as Zwack Unicum, a publicly listed company owned by the Zwack family with several partners.

“People think I showed faith in Hungary when not too many others did,” he told the New York Times in 1989. “They had been fed this picture of a fat capitalist who smoked cigars and beat up the workers, and they saw me, a skinny guy who doesn’t smoke, wears beat-up clothes and behaves more like the workers than the Communist bosses did.”

As his country transitioned to democracy, Mr. Zwack was invited to serve as ambassador. He accepted and renounced, with some reluctance, his U.S. citizenship.

In Washington, his first order of business was to discard the old brown curtains — relics of the socialist era — and repaint the embassy chancery that had become known as “the bunker.” In contrast with their communist predecessors, he and his wife, the British writer Anne Marshall, became fixtures on the Washington social scene.

But after seven months, Mr. Zwack was removed from office. In an interview with The Post, he attributed his removal to a conflict with his deputy chief of mission. The Post noted that, at a time when Hungary needed competent representation in Washington, neither Mr. Zwack nor his deputy had diplomatic experience.

High-profile internecine squabbling ensued. Mr. Zwack publicly called for the Hungarian foreign minister to resign, charging that the minister had intentionally misled the public about a controversial sale of Kalashnikovs to Croatia, which was seeking to break away from Yugoslavia.

“I am not made for the diplomatic life,” he told The Post at the time.

Peter Janos Zwack was born in Budapest on May 21, 1927, his son said. (In interviews, Mr. Zwack could be coy about revealing his exact age.)

Both sides of his family had converted from Judaism to Catholicism in 1917. His mother’s family owned steel mills; his father was an heir to the Zwack distillery. They lived a sumptuous lifestyle, with properties including two castles.

One of his father’s bridge partners was Raoul Wallenberg, the Swedish diplomat who was credited with rescuing tens of thousands of Hungarian Jews from Nazi persecution.

When Hungarian fascists stormed the cellar where the Zwacks had gone into hiding, the family managed to escape by alerting a Swedish diplomat across the street, who came to their aid. Mr. Zwack told the International Raoul Wallenberg Foundation that the Swede returned to the house with a machine gun and declared that the property was protected by the Swedish government.

After his ambassadorship, Mr. Zwack served for several years in the Hungarian parliament. His son Sandor Zwack succeeded him as chief executive of Zwack Unicum in 2008.

His marriage to his first wife, the former Iris Rogers, an American, ended in divorce. Survivors include his wife of 39 years, Anne Marshall Zwack of Bolgheri and Budapest; five children from his first marriage, Army Brig. Gen. Peter B. Zwack, now serving as a defense attache in Moscow, Gioia Zwack of New York City, Alexa Peterstam of Coral Gables, Fla., Iris Zwack of Newport, R.I., and John Zwack of Weston, Conn.; two children from his second marriage, Sandor Zwack and Izabella Zwack, both of Budapest; and 10 grandchildren.

“It’s unbelievable,” Mr. Zwack told the New York Times in 1989, reflecting on his life. “Preposterous. Wonderful.”