President Trump on Tuesday granted a pardon to Ross Ulbricht, the creator of the Silk Road drug marketplace and a cult hero in the cryptocurrency and libertarian worlds.

In doing so, Mr. Trump fulfilled a promise that he made repeatedly on the campaign trail as he courted political contributions from the crypto industry, which spent more than $100 million to influence the outcome of the election. A Bitcoin pioneer, Mr. Ulbricht, 40, was sentenced to life in prison without the possibility of parole in 2015, after he was convicted on charges that included distributing narcotics on the internet.

“I just called the mother of Ross William Ulbright to let her know,” Mr. Trump wrote in a post on Truth Social, misspelling Mr. Ulbricht’s name and making a reference to federal prosecutors in the Southern District of New York. “The scum that worked to convict him were some of the same lunatics who were involved in the modern day weaponization of government against me.”

In its nearly three years of existence, Silk Road, which operated in a shady corner of the internet known as the dark web, became an international drug marketplace, facilitating more than 1.5 million transactions, including sales of heroin, cocaine and other illicit substances. (The site generated over $200 million in revenue, according to authorities.) In court, prosecutors claimed that Mr. Ulbricht had also solicited the murders of people whom he considered threats — but acknowledged there was no evidence that the killings took place.

Despite his crimes, Mr. Ulbricht has remained popular with crypto enthusiasts because Silk Road was one of the first venues where people used Bitcoin to buy and sell goods. For years, his supporters have argued that his sentence was overly punitive and adopted the slogan “Free Ross” online and at industry gatherings.

“It’s hard to argue that Ross Ulbricht wasn’t the most successful and influential entrepreneur of the early Bitcoin era,” said Pete Rizzo, an editor at the news publication Bitcoin Magazine. “This is the industry banding together and saying, ‘We’re going to reclaim our own.’”

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