Towards the end of James T. Kirk's encounter with Trelane in 2267, Trelane's parents revealed themselves. Appearing as little more than indistinct, oddly pulsating, translucent green blobs, these beings chastised their errant son and removed him from the surface of Gothos. They spoke in rich, faintly echoing voices.
Most of their conversation was directed at Trelane, but Kirk was there to overhear every word of it. Kirk learned that Trelane was essentially a spoiled child who had created the planet of Gothos and everything on it for his own enjoyment, and everyone he sent down to Gothos were playmates to him. Trelane's parents presented a conflicting view: at one point, his mother referred to Humans as pets, telling Trelane that if he could not take proper care of his pets, he could not have them at all. (She might have been talking, hypothetically, about Humans.) Seconds later, however, his father told him, "They're beings, Trelane. They have spirit; they're superior." His mother then told him that when he grew up, he would understand. Trelane's arguments descended into childish whining, which drew a sharp rebuke from his father: if he did not stop whining, at once, then he would not be permitted to make any more planets.
After Trelane was gone, his parents apologized to Kirk, saying they would not have let Trelane intercept him if they had realized how vulnerable he was. Kirk's questions were essentially ignored, and Trelane's parents departed Gothos, promising to maintain the environment that Trelane had terraformed until Kirk left. There have been no known contacts with this civilization since this date.
Certain things can be inferred from Trelane's behavior and conversation he had with his parents. Their civilization evidently possesses incredible technical sophistication; the means to create entire planets, move them around, re-arrange the structure of matter nearly instantly on mental command, reshape environments, generate complex and powerful energy fields are all routine enough to be considered appropriate toys for an immature and spoiled child. (TOS: "The Squire of Gothos")