Roddenberry, a former pilot and police officer, had begun steadily writing for various TV series in the mid-1950s but longed to create his own show. After several of his ideas for pilots were rejected around Hollywood, he came up with the idea of a multiracial crew journeying through the stars on a large spaceship. Calling the show Star Trek, he wrote up a 16-page treatment on March 11, 1964, that would become the first documented blueprint for the series.
That treatment, which he presented to MGM and other studios until finally Desilu picked up the show, contains a number of conceptual elements that made it all the way to the eventual series when it debuted in 1966, as well as others that didn't quite carry through. Quite a few of the story ideas that Roddenberry came up with ended up on the original series as episodes, while the "parallel worlds" concept that allowed the show to travel to planets with Earth-like inhabitants and societies was first proposed in the pitch, as well.
Copies of the pitch have circulated on the Internet for a while; you can find one to peruse here, for instance. But let's take a look at some of the key ideas that Roddenberry dreamed up, and how they compare to what eventually made it to the screen ...
Robert April: The first captain of what became known as the Constitution-class U.S.S. Enterprise was not Christopher Pike or James Kirk, but Robert April, and it's April who is designated the lead in Roddenberry's original pitch. But Roddenberry's original description of the character featured many traits that found their way into Pike and Kirk, as well: a tendency to go quickly into action, a drive to put himself at risk before others, and a continual battle with the loneliness of command. (April later made his sole on-air appearance in the Star Trek: The Animated Series episode "The Counter-Clock Incident.")
Number One: This character -- an icy, logical, somewhat enigmatic woman who served as the ship's executive officer -- did make it into the first Star Trek pilot, "The Cage," where she was played by Majel Barrett (later Nurse Chapel on the show). Studio execs balked at a woman in a command position (of course they did), so Roddenberry took the emotionless aspect of the character and grafted it onto the ship's alien science officer, who was originally ...
The First Lieutenant: Called Spock even in his earliest incarnation, the captain's "right-hand man" was not the science officer at first. In fact, he wasn't even a Vulcan. Roddenberry surmised that he was "probably half Martian," with a reddish complexion, semi-pointed ears, and a "Satanic" look. Spock evolved quite a bit into his eventual identity -- although his "cat-like curiosity" about anything alien in nature stayed intact.
Other characters included Dr. Phillip "Bones" Boyce, a pragmatic doctor and reluctant space traveler who transformed more or less intact into Dr. Leonard McCoy; the Captain's Yeoman, named Colt, who the sexually preoccupied Roddenberry described as "very female, disturbingly so"; and Navigator Jose Ortegas, a young, hot-headed Latino whose DNA could probably be found in the show's Ensign Pavel Chekov.
The U.S.S. Yorktown: Roddenberry used this for the name of the ship at first, describing it as a "Cruiser-class" vessel capable of traveling via space warp at a top speed of ".73 of one light-year per hour." The ship's complement was 203 persons, as opposed to the 430 who found their way onto the Enterprise. The mission stayed pretty much the same: scientific investigation of the galaxy, security against unknown threats, and assistance to Earth colonies in the quadrant (Roddenberry did not mention the United Federation of Planets in the pitch). The treatment also postulated that the ship would carry galleys, recreation rooms, a sickbay, science labs, and a library, although we never did get to visit the latter (and no, that's not an early conception of the Yorktown above; a vessel with that name did show up in The Original Series and Star Trek IV: The Voyage Home).
The Transporter: There wasn't one, not at first. While the Yorktown was not built to land on planets itself (it "rarely" did, according to the treatment), away missions would use a "small recon rocket vehicle" to get themselves onto and off planets. While that vehicle morphed into the shuttlecraft and was still used in the show, somewhere along the line the idea of the transporter beam was developed, and with a cheap special effect became the de facto method of getting in and out of stories.
Weapons and Communication: While the ship itself was armed with laser beams for protection, the crew was originally going to carry rifles and pistols that fired either bullets, tranquilizer pellets, or explosive projectiles -- the phaser was yet to become the standard sidearm of starship crew members. The communicator, on the other hand, stayed pretty much the same from conception -- "a small transistor radio carried in a pocket" -- although the treatment made it clear that the device also served as a universal translator.
Roddenberry was remarkably consistent in how he saw stories developing: Sometimes the crew would land on a planet and find themselves in a situation there, while other segments would stay on the ship and revolve around a crew member or guest star. Within those 16 pages he generated some 25 story ideas -- basically a full season's worth -- although a number of those never made it to air. Here are a few examples:
"The Next Cage": The captain finds himself in an interplanetary zoo of sorts and offered a mate by his captors. This became the first pilot, "The Cage."
"The Day Charlie Became God": A man suddenly finds himself with incredible powers to do anything he wants ... the basis for the second Star Trek episode ever aired, "Charlie X."
"President Capone": The Enterprise comes upon a "parallel world" where criminal gangs rule and Al Capone leads them all. Sounds a bit like the second season's "A Piece of the Action," no?
"The Women": A group of women headed for a colony cause trouble for the men of the Yorktown. This morphed into the episode "Mudd's Women."
"Mr. Socrates": An odd premise in which the Yorktown visits a planet where the alien inhabitants recreate Earth's most famous figures -- Julius Caesar, Thomas Jefferson, Napoleon -- and then use them as combatants in Roman-like gladiatorial games. Diehard Trek fans will recognize strands of this idea in a number of episodes, including "Shore Leave," "Bread and Circuses," and "The Savage Curtain."
"The Perfect World": Pitched as an attack on Communism, in which Captain April and crew find themselves trapped on a totalitarian world that seems like paradise on the surface, this was another premise that found its way into a number of episodes, including "The Return of the Archons" and "This Side of Paradise."
"The Mirror": The Yorktown finds itself confronting an exact duplicate of the ship and the crew. Here is where the concept of the Mirror Universe took root, to later appear in nearly every series from Star Trek: The Original Series to Star Trek: Discovery.
"The Pet Shop"/"Kongo": Reflective of Roddenberry's wish to address social concerns on Star Trek, these two ideas end up sounding rather unfortunate and heavy-handed. In the first, the Yorktown arrives at a planet where women are dominant and men are treated as literal pets, while in the second, the ship comes upon a planet where it's still the "old plantation" days of the South -- except that whites are slaves and blacks are slave owners.
As mentioned earlier, one thing about Roddenberry's premise for Star Trek is that, despite quite a few changes along the way to the characters, ship, and other details, the original concept stayed the same throughout. Even as the franchise, in the form of Star Trek: Discovery and other projects, heads off in some surprising new directions more than 50 years later, that first pitch remains a remarkable document of a visionary idea.