Aaron Swartz, a wizardly programmer who as a teenager helped to develop a computer code that provided a format for delivering regularly changing Web content and in later life became an unwavering crusader to make that information free of charge, died in New York on Friday, a family member said.

Mr. Swartz was 26, and his death was due to suicide. His body was found by his girlfriend in his apartment in New York, his uncle, Michael Wolf, said on Saturday. He had apparently hanged himself, Mr. Wolf said.

As a 14-year-old, Mr. Swartz helped create RSS, the nearly ubiquitous software that allows people to subscribe to information from the Internet. But as he reached adulthood, Mr. Swartz became even more of an Internet folk hero to many because of his online activism to make many Internet files open to the public for free.

In July 2011, he was indicted in Boston on federal charges that he illegally gained access to JSTOR, a subscription-only online service for distributing scientific and literary journals, and downloaded 4.8 million articles and other documents, nearly the entire library.

Mr. Swartz formed a company that merged with Reddit, the popular news and information site. He also co-founded Demand Progress, a group that promotes online campaigns on social justice issues — including a successful effort, with other groups, to oppose a Hollywood-backed Internet piracy bill known as SOPA, the Stop Piracy Act.

But he also found trouble when he took part in efforts to release information to the public that he felt should be freely available. In 2008, he took on Pacer — or Public Access to Court Electronic Records, the repository for federal judicial documents. The database charges 10 cents a page for documents; activists like Carl Malamud, the founder of public.resource.org, have long argued that such documents should be free since they are produced at public expense. Joining Mr. Malamud’s efforts to make the documents public by posting legally obtained files to the Internet for free access, he wrote an elegant little program to download 20 million pages of documents from free library accounts, or roughly 20 percent of the enormous database.

The government abruptly shut down the free library program, and Mr. Malamud feared that legal trouble might follow, even though he felt they had violated no laws. As he recalled in a newspaper account of the events, “I immediately saw the potential for overreaction by the courts.” He recalled telling Mr. Swartz, “You need to talk to a lawyer. I need to talk to a lawyer.”

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