"The Hundred Days of the Dragon" is the second episode of the original The Outer Limits television show. It first aired on 23 September 1963, during the first season.
An Asian government develops a reliable means of changing a person's physical appearance, and uses it to replace a U.S. presidential candidate with a spy.
"Somewhere south of the Mongolian border and north of the Tropic of Cancer, in that part of the world we call the Orient, a slumbering giant has shaken itself to wakefulness. Passed over in most histories as a nation forgotten by time, its close-packed millions in the short span of twenty years have been stirred to a fury by one man: Lee Ching Sung. A benevolent despot in his homeland, Sung stands as an irresponsible threat to peace in the eyes of the rest of the world. William Lyons Selby, candidate for the presidency of the United States, predicted by every poll, survey, and primary to be a certain winner in the forthcoming election."
An unspecified Asian government plans to take over America by infiltrating and substituting all the officials at the White House. During the presidential campaign, William Lyons Selby (the candidate predicted to win the next election) is murdered and then replaced by a lookalike spy. Selby is elected, and the impostor assumes the office of the President of the United States.
He fools the nation at large during his first few months in office, but his daughter, Carol, soon begins to suspect that the man in the White House is not her father. She voices her concerns to the Vice President, Ted Pearson. He disbelieves her at first, until he is targeted for substitution by an assassin who breaks into his home during their conversation. Already in the guise of Pearson, he is chased off before he can commit the act.
Now convinced that Carol's story is valid, Pearson informs the head of the Secret Service detail assigned to the President of the plot, and the suspicion that Selby is an impostor. After several failed attempts by the Secret Service in identifying Selby through dental records and other means, the leader of the Asian government confers with his spy at the White House prior to a planned summit meeting, where he reveals the second phase of their operation to substitute various cabinet members, heads of state, and private industry tycoons. When Selby arranges a second attempt at replacing his Vice President, the perpetrators are captured, brought before the President during a state reception and exposed, along with Selby, himself, with the real Pearson arresting and then charging him with murder and attempting to overthrow the United States government.
"To Theodore Pearson not even so monstrous a crime as the assassination of William Lyons Selby justifies an act of war, because there is no war as we know it, only annihilation. A great American has been killed in the service of his country. Now it is the job of those who continue to serve to carry on guarding our freedom with dignity and unrelenting vigilance."
- Sidney Blackmer – as William Lyons Selby and doppelganger
- Phillip Pine – as Theodore Pearson
- Joan Camden as Ann Pearson
- Nancy Rennick as Carol Selby Conner
- Richard Loo as Li Chin-Sung
- Mark Roberts as Dr. Bob Conner
- Aki Aleong – as Dr.Su Lin
- Clarence Lung as Major Ho Chi Wong
- James Hong as Wen Lee
- James Yagi as Li Kwan
- Bert Remsen  as Frank Summers
- Dennis McCarthy as Carter
- Richard Gillings as Briggs
- Robert Brubaker as Bryan
- Eugene Chan as Oriental in Hotel
- Henry Scott – as FBI Agent Marshall
- Vic Perrin as Voice of Mr. Schumacher
- Leslie Stevens – as the Election Returns Commentator (uncredited)
- The plot bears some similarity to that of the novel The Manchurian Candidate by Richard Condon.