Bela Okmyx was a prominent 23rd century Iotian. He was the boss of the Northside Territory, the largest territory on Sigma Iotia II. After a cultural intervention in 2268, he was installed top boss in a syndicate uniting all territories on the planet. Like other Iotians of his era, his personality was modeled on Earth's Chicago gangster period.
In 2268, the Enterprise visited the planet to update its progress. Okmyx offered to cut Kirk in on the action, if Kirk helped him take over the planet by providing him with "heaters". When Kirk refused the request, he and Spock were taken hostage and Okmyx threatened to kill them and have their dead bodies sent back up to the ship if they didn't get him the "heaters" within eight hours. Kirk, however, was able to escape.
Kirk was able to intervene and end the conflict between the bosses when he had the USS Enterprise fire phasers on stun in the surrounding area to demonstrate the power of the "Feds." Impressed by the display, Okmyx claimed to be a peaceful man at heart and sick and tired of the hits. Other bosses were likewise convinced by the show of power, and agreed to Federation control with Okmyx as the top boss and Jojo Krako, his former rival, as his lieutenant.
Okmyx was a pool player, and claimed to distill drinks. He sometimes utilized double negatives. During his reign of Northside Territory, posters of Okmyx were on display in its streets. (TOS: "A Piece of the Action")
Bela Okmyx was played by actor Anthony Caruso. His surname has appeared in many subsequent texts, including the Star Trek Concordance, The Star Trek Compendium, the Star Trek Encyclopedia (4th ed., vol. 2, p. 117), and StarTrek.com as the way it was pronounced throughout the episode: "Oxmyx."  The correct spelling, as seen on posters throughout the episode, was in fact "Okmyx."
The "Okmyx" spelling is also found in the "Final Draft" of the shooting script, dated 30 October 1967 – with revised pages dated 31 October 1967. Although pronunciation is provided for other characters in this episode, no such guidance is provided for "Okmyx." The end credits simply credit the character as "Bela."
Okmyx might have been single, based on Krako's boast that he could not go on a date with a broad without Krako knowing it.
The character appeared again in an issue of DC Comics' second volume comics series, "... Let's Kill All the Lawyers!", where he revealed at Kirk's trial that the captain's cut of Iotia's "action" was still being skimmed for him. Okmyx also returned Leonard McCoy's communicator (which the doctor had left behind on Iotia), saying that the Iotians didn't do anything with the device and just put it away for safekeeping.