BOSTON — Halfway around the world from Tahrir Square in Cairo, an aging American intellectual shuffles about his cluttered brick row house in a working-class neighborhood here. His name is Gene Sharp. Stoop-shouldered and white-haired at 83, he grows orchids, has yet to master the Internet and hardly seems like a dangerous man.

But for the world’s despots, his ideas can be fatal.

Few Americans have heard of Mr. Sharp. But for decades, his practical writings on nonviolent revolution — most notably “From Dictatorship to Democracy,” a 93-page guide to toppling autocrats, available for download in 24 languages — have inspired dissidents around the world, including in Burma, Bosnia, Estonia and Zimbabwe, and now Tunisia and Egypt.

When Egypt’s April 6 Youth Movement was struggling to recover from a failed effort in 2005, its leaders tossed around “crazy ideas” about bringing down the government, said Ahmed Maher, a leading strategist. They stumbled on Mr. Sharp while examining the Serbian movement Otpor, which he had influenced.

When the nonpartisan International Center on Nonviolent Conflict, which trains democracy activists, slipped into Cairo several years ago to conduct a workshop, among the papers it distributed was Mr. Sharp’s “198 Methods of Nonviolent Action,” a list of tactics that range from hunger strikes to “protest disrobing” to “disclosing identities of secret agents.”