Star Trek is a science fiction television series created by Gene Roddenberry in the 1960s and aired between September 8, 1966 to September 2, 1969, with a total of 79 episodes produced. Although cancelled after its short run, the program was placed in syndication and spawned a strong fan following. The success of the program was followed by five additional television series and ten theatrical movies. The Guinness Book of Records lists it as having the largest number of spinoffs. To distinguish this first series from the sequels which followed (all of which comprise the Star Trek universe or franchise), it has acquired the retronym Star Trek: The Original Series (sometimes shortened to ST:TOS or TOS).

Set in a utopian vision of the 23rd century, Star Trek follows the adventures of the starship Enterprise and her crew, led by William Shatner as Captain James T. Kirk, Leonard Nimoy portraying his first officer, Mr. Spock. Shatner's voiceover at the beginning of each episode—with the exceptions of both pilots, "The Cage" and "Where No Man Has Gone Before"—stated the ship's purpose:

Space, the final frontier. These are the voyages of the starship Enterprise. Its five-year mission: to explore strange new worlds, to seek out new life and new civilizations, to boldly go where no man has gone before.

When Star Trek debuted on NBC in 1966, it was not successful; ratings were low and advertising revenue was lackluster. For the show's second season, it was moved to Friday nights at 8:30 P.M. and the threat of cancellation loomed. The show's devoted fanbase conducted an unprecedented campaign, petitioning NBC to keep the show on the air, succeeding in gaining a third season. But after the show was moved from 8:30 P.M. to 10 P.M. on Fridays, ratings remained poor. The series was cancelled at the end of its third season.

A longtime fan of science fiction, in 1960 Roddenberry put together a proposal for Star Trek, a science fiction television series set on board a large interstellar space ship dedicated to exploring the galaxy. Some influences Roddenberry noted were A. E. van Vogt's tales of the Space Beagle, Eric Frank Russell's Marathon stories, and the 1956 science fiction film Forbidden Planet. Roddenberry also had extensive experience in writing westerns that were particularly popular televison fare at the time, and pitched the show to the network as a "Wagon Train to the stars."

In 1964, Roddenberry secured a three-year development deal with leading independent TV production company Desilu (founded by comedy stars Lucille Ball and Desi Arnaz). In Roddenberry's original concept, the protagonist was named Captain Robert April of the "S.S. Yorktown". Eventually, this character became Captain Christopher Pike. The first pilot episode, "The Cage", was made in 1964, with actor Jeffrey Hunter in the role of Pike.

Roddenberry envisaged a multi-racial and mixed-gender crew, based on his assumption that racial prejudice and sexism would not exist in the 23rd century at a time when racial segregation was still firmly entrenched in many areas of the United States. He also included recurring characters from alien races, including Spock, who was half human and half Vulcan, united under the banner of the United Federation of Planets.

Other innovative Star Trek features involved solutions to basic production problems. The idea of the faster-than-light warp drive was not new to science fiction, but it allowed narrative device that permitted the Enterprise to quickly traverse space. The matter transporter, where crew members "beamed" from place to place, solved the problem of moving characters quickly from the ship to a planet, a spacecraft landing sequence for each episode being prohibitively expensive.

The Star Trek pilot was first offered to the CBS network, but the channel turned it down for the more mainstream Irwin Allen production, Lost In Space. Star Trek was then offered to NBC, and executives were favorably impressed with the concept and made the highly unusual decision to commission a second pilot: "Where No Man Has Gone Before". Only the character of Spock (played by Leonard Nimoy) remained from the original pilot, and only two cast members (Majel Barrett and Leonard Nimoy) carried on to the series. Much of the first pilot's footage was utilized into a later two-part episode, "The Menagerie".

In the second pilot, the main characters, Captain Kirk (William Shatner), chief engineer Lieutenant Commander Scott (James Doohan) and Lieutenant Sulu (George Takei) were introduced. Chief medical officer and the captain's confidante Dr. Leonard McCoy (DeForest Kelley) (a Dr. Piper was present on the pilot) , Yeoman Janice Rand (Grace Lee Whitney) and communications officer Lieutenant Uhura (Nichelle Nichols) were introduced later. Roddenberry's inclusion of the Asian Sulu and black Uhura was a bold move when most television characters of the time were white.

Members of Roddenberry's production staff included art director Matt Jefferies. Jefferies designed the Enterprise; his contribution was commemorated in the so-called Jefferies tube, which became a standard part of the (fictional) design of Federation starships. Jefferies' starship concepts arrived at a final saucer-and-cylinders design that became a template for all subsequent Star Trek space vehicles. Jefferies also developed the main set for the Enterprise bridge (based on an original design by Pato Guzman) and used his practical experience as a WWII airman and his knowledge of aircraft design to come up with a sleek, functional, ergonomic bridge layout. Costume designer William Ware Theiss created the look of the Enterprise uniforms and the risqué costumes for female guest stars. Artist and sculptor Wah Chang, who had worked for Walt Disney, was hired to design and manufacture props: he created the flip-open communicator, the portable sensing-recording-computing tricorder and the phaser weapons.

The series introduced viewers to many ideas which have become common in science fiction films: warp drive, teleportation, wireless hand-held communicators and scanners, directed energy weapons, desktop computer terminals, laser surgery and computer speech synthesis. Although these concepts had numerous antecedents in sci-fi literature and film, they had never before been integrated in one presentation. Even the ship's automatic doors were a novel feature in 1966.

- From Wikipedia