Francis Xavier Waldron (August 10, 1905 – January 31, 1961), best known by the pseudonym Eugene Dennis and Tim Ryan,[1] was an American communist politician and union organizer, best remembered as the long-time leader of the Communist Party USA and as named party in Dennis v. United States, a famous McCarthy Era Supreme Court case.

Dennis became General Secretary of the party after the expulsion of Earl Browder and was a staunch supporter of the Moscow line.

As Dennis and his co-accused had never openly called for the violent overthrow of the United States government, the prosecution depended on passages from the works of Karl Marx and Vladimir Lenin that advocated revolutionary violence and on the testimony of former members of the party who claimed Dennis and others had privately advocated the use of violence.

The Court later scaled back its Dennis opinion in Yates v. United States and rendered the broad conspiracy provisions of the Smith Act unenforceable.

Though never charged with any act of espionage, Dennis was identified in the Venona project as being a source for Soviet intelligence in the United States during World War II.