The company would eventually count among its clients Alexander Lukashenko, the dictator of Belarus; the Sultan of Brunei; repressive regimes in Bahrain and Egypt; and Oscar Pistorius, the Olympic sprinter, just after he had been accused of murdering his girlfriend.

When asked by Financial Times if he had ever declined to represent anyone, he named Robert Mugabe, the former prime minister of Zimbabwe; the Labour Party; and six Russians who had been slapped with sanctions by the European Union.

“I don’t think I’ve handled any dubious characters,” he told the BBC in 2017. “I could defend them all.”

For General Pinochet, who ruled Chile for decades, Bell Pottinger coined the phrase “Reconciliation, not retribution” and played up his poor health after he was placed under house arrest in London on an extradition warrant for human rights violations issued by Spain.

After a legal battle that ended in 1990, General Pinochet was released on the grounds that he was medically unfit for trial. Bell Pottinger’s fees were paid by the Pinochet Foundation.

A swaggering figure who wore Armani suits and drove a red Ferrari, Mr. Bell sought out and relished attention. “I enjoy being stared at,” The Telegraph once quoted him as saying. He was such an avid smoker of Dunhill cigarettes — 80 a day, friends say — that he had a bed installed in his office so he could circumvent national health rules and claim the space as his home.

“For all his many flaws, he was a titan of the P.R. industry,” said Francis Ingham, director general of the Public Relations and Communications Association, a trade group. “He courted controversy and controversial clients, and although there are many who disapproved of some of his clients, I think everyone would acknowledge his enormous talents.”