Warren J. Hinckle, III was a well-known columnist and provocateur best known as the editor of Ramparts magazine and a vocal (and at times gonzo) proponent of left politics. His FBI file pertains chiefly to an investigation into an advertisement placed in 1981 seeking to recruit volunteers for an American brigade of the IRA, and also contains excerpts of his writing on Cuba.
Muckrock has posted a more extensive look into the contents of Hinckle's FBI file.
New York Times obit: Warren Hinckle, Ramparts Editor Who Embraced Gonzo Journalism, Dies at 77