a state actor is a person who is acting on behalf of a governmental body, and is therefore subject to regulation under the United States Bill of Rights, including the First, Fifth and Fourteenth Amendments, which prohibit the federal and state governments from violating certain rights and freedoms.
Although at first blush the term would seem to include only persons who are directly employed by the state, the United States Supreme Court has interpreted these amendments and laws passed pursuant to them to cover many persons who have only an indirect relationship with the government. Controversies have arisen, for example, over whether private companies that run towns (the "company-town") and prisons (traditionally a state function) can be held liable as state actors when they violate fundamental civil rights. This question remains unresolved, but the Supreme Court has held private citizens to be liable as state actors when they conspire with government officials to deprive people of their rights.