Arthur J. Finkelstein, whose sharp, relentless attack ads helped elect dozens of conservative political candidates in the United States and abroad and made him a kingmaker in Republican circles for decades, died Aug. 18 at his home in Ipswich, Massachusetts. He was 72.

The cause was metastasized lung cancer, his family said in a statement.

Finkelstein cultivated a reputation as a shadowy behind-the-scenes figure, seldom granting interviews and rarely drawing attention to himself in public – all of which lent him a mystique as a pollster, campaign manager and ruthless operative in electoral politics.

He became an influential political power broker in the 1970s who helped propel the careers of Republican senators such as James L. Buckley (N.Y.), Jesse Helms (N.C.), Orrin G. Hatch (Utah) and Alfonse D’Amato (N.Y.), as well as Israeli Prime Minister Benjamin Netanyahu. He also fostered a generation of Republican political consultants whose careers began on his campaigns.

Finkelstein was considered a master at developing simple campaign messages, which were repeated in such a steady barrage of negative television commercials that he was sometimes called the “merchant of venom.” As much as anyone, he was responsible for making the word “liberal” a political slur.

He was also something of a political conundrum – especially after it was revealed in 1996 that his private life as a gay man was in sharp contrast to the views of some of the conservative firebrands he helped elect. Helms, for instance, often railed against the “homosexual movement,” which he said “threatens the strength and the survival of the American family.”

In 1996, New York Times columnist Frank Rich described Finkelstein as someone who “sells his talents to lawmakers who would outlaw his family’s very existence.”

Finkelstein was credited with helping raise Ronald Reagan’s national profile during the 1976 Republican primary campaign. Ultimately, the nomination went to President Gerald R. Ford, who lost the general election to Democrat Jimmy Carter.

Reagan’s insurgent campaign against a sitting president laid the groundwork for his overwhelming presidential victory in 1980. Finkelstein was seen as one of several Republican strategists, including Roger Ailes, Lee Atwater and Charlie Black, who were instrumental in helping shape what became known as the Reagan Revolution.

“Without Arthur Finkelstein, Ronald Reagan might never have become president of the United States,” historian and Reagan biographer Craig Shirley wrote on the website of National Review magazine in January 2017.

During Reagan’s eight years in the White House, Finkelstein was an informal adviser to the administration and managed congressional and gubernatorial campaigns across the country.

“He uses a sledgehammer in every race,” political scientist Darrell M. West told the Boston Globe in 1996.