Timothy C. May, a physicist, polemicist and cantankerous advocate of internet privacy who helped start a movement aimed at protecting the privacy of individuals online, died on Dec. 13 at his home in Corralitos, Calif. He was 66.

The Santa Cruz County Sheriff-Coroner’s office confirmed his death but said that the cause had not yet been determined.

As the rabble-rousing leader of a group called the Cypherpunks, Mr. May, in his writings, foreshadowed and influenced many of the concerns about privacy and government control that have come to dominate the internet age.

In the one-page Crypto Anarchist Manifesto, which he wrote in 1988, Mr. May said, “Just as the technology of printing altered and reduced the power of medieval guilds and the social power structure, so too will cryptologic methods fundamentally alter the nature of corporations and of government interference in economic transactions.”