John Perry Barlow, an influential champion of an open internet and lyricist for the rock band Grateful Dead, died Wednesday at the age of 70.

Barlow's death was announced by the Electronic Frontier Foundation, the San Francisco-based digital rights group he cofounded in 1990 with John Gilmore and Mitch Kapor. A possible cause of death was not immediately available, but Barlow had been hospitalized periodically after suffering a heart attack in 2015.

Barlow wrote extensively for various publications about the power of the internet, helping to establish the idea that we need to wrestle with the internet not just as a technological phenomenon, but also as a cultural, political and legal one.

He is probably best remembered for his "A Declaration of Independence of Cyberspace," a 1996 paper that argued against governmental influence on the internet. Barlow penned the paper as a rebuttal to the recently enacted Communications Decency Act of 1996, which he saw as a threat to the independence of cyberspace.

"Governments of the Industrial World, you weary giants of flesh and steel, I come from Cyberspace, the new home of Mind. On behalf of the future, I ask you of the past to leave us alone. You are not welcome among us. You have no sovereignty where we gather," Barlow wrote.

EFF Executive Director Cindy Cohn credited Barlow's vision and leadership with helping major parts of the internet to exist and thrive.

"He always saw the Internet as a fundamental place of freedom, where voices long silenced can find an audience and people can connect with others regardless of physical distance," Cohn said in a statement. "Barlow knew that new technology could create and empower evil as much as it could create and empower good. He made a conscious decision to focus on the latter."

Born in Wyoming on Oct. 3, 1947, Barlow graduated with a degree in comparative religion from Wesleyan University.

In addition to his cyber activism, Barlow was a poet, essayist and an early lyricist for the rock band Grateful Dead, thanks to a friendship he formed as a teenager with founding member Bob Weir. His songs for the band included "Cassidy," "Estimated Prophet" and "Black-Throated Wind."

He also served as a Fellow Emeritus at Harvard University's Berkman Center for Internet and Society.

Barlow is survived by his wife Elaine and their three daughters.

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