| "The Enemy Within" | |
|---|---|
| Star Trek: The Original Series episode | |
| Episode no. | Season 1 Episode 5 |
| Directed by | Leo Penn |
| Written by | Richard Matheson |
| Featured music | Sol Kaplan |
| Cinematography by | Jerry Finnerman |
| Production code | 5 |
| Original air date | October 6, 1966 |
| Guest appearances | |
| |
"The Enemy Within" is the fifth episode of the first season of the American science fiction television series, Star Trek. Written by Richard Matheson and directed by Leo Penn, it first aired on October 6, 1966.
In the episode, while beaming up from planet Alpha 177 a transporter malfunction causes Captain Kirk to be split into two people, one "good," but indecisive and ineffectual; the other "evil," impulsive and irrational.