"I know, I know. A thousand questions. But first, the tranya."
Balok encountered the USS Enterprise while it was midway through a star mapping mission. He used a puppet of a bluish, cat-eyed alien, that wavered and rippled on the Enterprise's viewscreen, to fool the starship's crew into believing the puppet was named Balok and was in control of the Fesarius. Balok apparently condemned the crew as warlike, because they had been forced to destroy a marker buoy, and repeatedly threatened them with the consequences, such as seemingly planning to destroy the Enterprise.
After Balok's pilot vessel (a much smaller craft, launched from the Fesarius) was damaged by the Enterprise and Captain James T. Kirk beamed aboard with a landing party that also included Doctor Leonard McCoy and Crewman Dave Bailey, the real Balok divulged the truth to his visitors; he revealed his use of the puppet and that the entire encounter had been an elaborate test of character and ethics. Balok was amused by having manipulated the Enterprise crew with the puppet, which he called "Mr. Hyde to my Jekyll", and which he commonly used to frighten and intimidate others. He shared a drink of tranya with the landing party, and gave them a tour of his ship.
As the Fesarius had a crew of only one, Balok was the only representative of the First Federation encountered by Starfleet so far. He admitted he was lonely, so Kirk left Crewman Bailey with Balok, for an exchange of cultures and ideas. Balok gave all three visitors a tour of his small pilot vessel, before Kirk and McCoy departed. (TOS: "The Corbomite Maneuver")
Originally (in an outline called "Danger Zone", from March 1966), Balok was an avian who initially told the Enterprise crew that he was the liaison officer of the Fesarius. Balok lost consciousness, but was saved by the Enterprise medical staff. Aboard the Enterprise at the end of the story, he revealed he was actually the commander of the Fesarius and shook Kirk's hand with his talons, in a friendly gesture. Before leaving the Enterprise, Balok extended an open invitation for Kirk and his officers to visit the Fesarius at any time. Balok was also described as having more attractive plumage than two of his subordinates, who were of the same species as him.
In the second draft outline of "The Corbomite Maneuver", the character was portrayed as acting in much the same way. However, Balok was no longer an avian. Instead, he was described as a non-descript alien who was taller than his fellows and who shook hands with Kirk (though a question mark indicated that there was still some uncertainty as to whether Balok even had hands). Another change affecting Balok was the introduction of the concept of corbomite; Balok was insistent that no such substance existed, though at the end of the story, he admitted he was unsure as to whether it did or not.
Jerry Sohl developed Balok further while trying to devise the conclusion to the episode "The Corbomite Maneuver". He later commented, "How the hell were they [the Enterprise crew] going to get out of this one? And then we added the fellow at the end, which was so much like the end of many of my novels, where a little kid is behind the whole thing. That tickled Gene Roddenberry." (Starlog #136, p. 69) This idea was first established in the third draft outline of "The Corbomite Maneuver", in which Balok was the only member of his species to appear – doing so only at the end of the story, using a puppet before that point – and was simply described as "a midget by Earth standards." The outline also related some uncertainty over whether he could smile. Also, rather than coming aboard the Enterprise at the end of the episode, Balok met Kirk, Spock, the doctor from the Enterprise and two of his aides onboard Balok's pilot vessel. Without shaking hands with Kirk, Balok revealed that he himself was the Fesarius' commander, extended his open invitation for the Enterprise crew to visit the Fesarius, and admitted to being unsure if corbomite really existed.
In the first draft script of "The Corbomite Maneuver" (submitted in April 1966), Balok was described as "tiny by earth standards, almost childlike (a child actor), soft, warm, almost lovely in his tiny simplicity." In the final draft of the script (dated 3 May 1966), Balok was characterized as "a veritable child of a man, pudgy, soft-looking, warm and cuddly, wearing a robe of fine cloth, [...] smiling cherubically." The second revised final draft of the script (dated 20 May 1966) added to this description by commenting that Balok was to be "less than four feet tall." A later description in both the final draft and the second revised final draft stated, "Balok's voice, deep and commanding, belies his small stature."
In a memo Robert Justman sent John D.F. Black (on 21 April 1966), Justman proposed that, rather than staying on his own ship and being visited there by officers from the Enterprise, Balok should come aboard the Enterprise at the end of the episode, a potentially cost-cutting but ultimately unrealized story point.
In the first draft and final draft of the teleplay for "The Corbomite Maneuver", Balok met only Kirk and McCoy from the Enterprise. In at least the final draft, though, he allowed them to contact Spock, who was on the bridge of the Enterprise. At one point in the same draft of the script, Balok reacted dismally to being asked what would have happened if they hadn't tried to save him. The scripted stage directions concerning Balok's gloomy response remarked, "The merest shadow of some of Balok's former fierceness plays over his small features and we get a glimpse of the strength that lies beneath. It passes." All of these elements were excluded from the script by the time the second revised final draft of the teleplay was issued, that version also including Balok meeting Bailey and arranging for him to stay.
At first, the casting requirements for the role of Balok were different than they eventually became. In retrospect, Casting Director Joseph D'Agosta offered, "As I recall we had to get someone who could play young, but was an adult." (Cinefantastique, Vol. 27, No. 11/12, p. 60) This, though, was problematic. In the aforementioned memo Robert Justman wrote John D.F. Black (on 21 April 1966), Justman critiqued, "Although I like the conception of the character called Balok, there could be one drawback with regard to this. The part should be played by a midget or a dwarf. There aren't many actors with these physical characteristics who could handle the job. And certainly the few that are available are rather well known to our audience."
NBC Manager of Film Programming Stan Robertson essentially came up with the notion of hiring two different actors to play Balok, with one of them voicing the part while the other's physical performance would be used. Robertson submitted this concept in a letter he wrote John D.F. Black (on 2 May 1966). However, Robertson's idea was actually to cast a large actor to appear as Balok's puppet, and the voice of "a smaller person" for that same role, then for the latter performer to appear as the real Balok in the episode's conclusion. Regarding the real Balok, he commented, "When we actually meet him in person, at this time we could see that he is a 'Michael Dunn' type person. Obviously, as you pointed out, we will be giving the whole thing away if we show Balok at the outset to be a 'Dunn' type character." In fact, Michael Dunn himself eventually guest starred, two years later, in "Plato's Stepchildren".
During a casting meeting for "The Corbomite Maneuver", much discussion was concentrated on how Balok, who was conceived as being three-and-a-half feet tall, should look. Multiple strange ideas were suggested and considered, in an effort to resolve this problem. After quietly listening to the proposed ideas, Gene Roddenberry finally commented, "I think if you cast anyone over seven years old, you're in trouble." (The Making of Star Trek, p. 348) Concerning the casting of a child actor to appear as Balok with an adult actor providing the character's voice, Richard Arnold, who worked as a research consultant for Roddenberry, commented, "Yeah, that was Gene pushing the envelope. It was the sort of thing that good science fiction did." ("Inside the Roddenberry Vault, Part I", Star Trek: The Original Series - The Roddenberry Vault special features)
Clint Howard was found by Joe D'Agosta, who added, "I met Clint Howard through the agents as a type, a dwarf-like type." (Cinefantastique, Vol. 27, No. 11/12, p. 60) Howard himself explained, "The Star Trek audition entailed a lot of learning of dialogue, because although they eventually voiced my character, I learned the dialogue." ("Inside the Roddenberry Vault, Part I", Star Trek: The Original Series - The Roddenberry Vault special features) The day after Gene Roddenberry advised casting an actor under the age of seven as Balok, D'Agosta brought Howard, who was then aged seven, onto the Desilu lot. He then auditioned for the role. (The Making of Star Trek, p. 349) "I remember his interview as being kind of overwhelming," D'Agosta admitted, "because he had the built-in cry-baby sneer on his face." (Cinefantastique, Vol. 27, No. 11/12, p. 60) Nonetheless, Howard was offered the role. ("Inside the Roddenberry Vault, Part I", Star Trek: The Original Series - The Roddenberry Vault special features) He was cast in the part immediately after auditioning. (The Making of Star Trek, p. 349) Decades later, Howard commented, "The character of Balok, interesting character because of the way he would taunt the Enterprise, and then the choice of hiring a child, almost with a cherub face, with an adult voice, this kid face, having played this game of death poker with Captain Kirk, was an odd [but successful] choice." ("Inside the Roddenberry Vault, Part I", Star Trek: The Original Series - The Roddenberry Vault special features)
A voice-over performer was additionally sought for the role of Balok. In a memo Robert Justman sent Gene Roddenberry (on 4 August 1966), Justman wrote, "I spoke last night with Joe D'Agosta with regard to bringing in some people to be interviewed for Looping Balok's voice in 'The Corbomite Maneuver'. It is important that we set this actor or actress as soon as possible, so that we can do the necessary looping this coming Tuesday morning, August 9, 1966. This will enable us to take advantage of the Looping Stage, as we have to do other Loops for the show currently in progress that day anyway. We should have someone cast by Friday, or Monday at the latest."
Clint Howard was originally asked if, to play Balok, he was willing to shave his hair off, but both he and his father said no. (The Making of Star Trek, p. 349; These Are the Voyages: TOS Season One) Decades later, Howard recalled, "Now, [that] wouldn't be an issue, but back then... hell, yeah, it was an issue! They went and put a bald cap on me." ("Inside the Roddenberry Vault, Part I", Star Trek: The Original Series - The Roddenberry Vault special features) The make-up Howard wore for the role of Balok was designed to be minimal and inexpensive. The bald cap was premade from plastic by John Chambers. It was glued around Howard's hairline with spirit gum. Once dry, the bald cap's edges were dissolved with a little amount of acetone, making the seam between the cap and the actor's head nondistinguishable on camera. To establish the overall skin tone, a tan cream base was sponged over Howard's bald cap and face. As a final touch, a pair of extremely bushy eyebrows were also employed to exaggerate the actor's alien look. These bushy eyebrows, almost belying the character's childlike appearance, were hand-laid on the actor's face, then affixed with glue. The make-up made Balok look noticeably different from the Enterprise crewmembers, but was entirely non-threatening in comparison with his puppet. (Star Trek: Aliens & Artifacts, p. 35) (Make-up test shots of Howard as Balok, from the Gene Roddenberry Collection at UCLA, can be seen here: )
One challenge Clint Howard found with portraying Balok was having to drink the character's tranya, which – according to the actor – was grapefruit juice, a beverage he detested in his childhood. "I saw the guy pouring it from the carton, so I went over to my dad and said, 'Dad? Come on. I mean, [...] grapefruit juice makes me gag. Can you get them to change it to apple juice? I love apple juice.' And my dad said, 'We're not going to change it. Just think about this as an acting challenge. Drink it and just act like you really enjoy it' [....] Probably the most difficult acting I did back then was to drink that stuff," Howard laughed. (Star Trek: Communicator issue 115, p. 65)
It was because Balok was meant to be an adult alien, despite having a childlike appearance, that Clint Howard's vocal track was deleted in post-production and the character was instead voiced by Walker Edmiston. (Star Trek: The Original Series 365, p. 34) Edmiston later recalled, "We'd tried a number of different things and then we just went to one of those very soft, child-like, ethereal vocals. It was more in timing and attitude than in voice. That's what's so important in creating a voice for creatures and all types of unearthly things. You have to analyze what it is, what they do, are they large, small, and what is the process behind them. And physically, of course, that makes a lot of difference as he had those big teeth and a weird little smile." (Starlog #58, p. 21)
Seeing Balok in "The Corbomite Maneuver" was one of Star Trek author David R. George III's earliest memories of watching Star Trek. In his adulthood, he remarked, "I remember understanding that the alien whom the Enterprise crew encountered was not all that different from any human being – and not simply because it turned out that Balok actually appeared quite human, and not at all like his spooky doppelgänger – but because he lived and thought and felt in a recognizable way. I really think that helped form an empathy within me, an ability to see things from other people's points of view." 
The fact Clint Howard appeared as Balok was referenced during an audition the actor later had, when he was about twenty-two or twenty-three years old, with renowned filmmakers George Lucas and Francis Ford Coppola. Howard remembered, "[Lucas] looks at me and he goes, 'Commander Balok, Corbomite Maneuver.'" (Star Trek Monthly issue 49, pp. 50 & 51) Lucas' reference to the character was the first thing he said to Howard. (Star Trek: Communicator issue 115, p. 65) "It absolutely blew me away," the actor recalled. (Star Trek Monthly issue 49, p. 51) In reply, Howard felt he wanted to yell at Lucas to "get a life." (Star Trek: Communicator issue 115, p. 65; Star Trek Monthly issue 49, p. 51)
Clint Howard later reprised his role as a grown Balok as part of Comedy Central's 2006 roast of William Shatner. In it, Howard portrayed Balok as being an alcoholic, addicted to tranya. As with the episode, Balok's voice was again dubbed in by another actor.
In the Star Trek: Voyager short story "Ambassador at Large" from the anthology book Strange New Worlds, Balok explored the Alpha Quadrant with Bailey for around twenty years. After that, the two decided to continue their explorations into the Delta Quadrant. Their next contact with anyone from the Federation came in 2373 when Captain Kathryn Janeway and the crew of the USS Voyager rescued Bailey from the Mondasians. In gratitude, Balok escorted Captain Janeway on a tour of the Fesarius.