In 2269, the USS Enterprise discovered their homeworld, and Lucien was the first to greet them. He did so, however, under the condition (and the ruse) that the other Megans would not learn of the Humans' presence at Megas-Tu.
Following the discovery of the Human presence, Lucien and the Enterprise crew were placed on a Salem-type trial to answer for the crimes of their forefathers. Lucien was also placed on trial for welcoming the Humans to their planet, with the threat of spending eternity in limbo.
Kirk was willing to sacrifice himself to save Lucien, despite his previous aliases and reputation from his time on Earth. In doing so, Kirk proved to the Megans that Humans had changed over the past six centuries. The Megans informed them that they had passed the Megans' test and welcomed them to their planet with open arms. (TAS: "The Magicks of Megas-Tu")
In the script for "The Magicks of Megas-Tu", Lucien is initially described as "an alien, half-goat, half-man, complete with cloven hooves, horns, and tail. He is the image of all the goatgods of supernatural mythology, bearded and broad, with a strange red glint in his eyes. He looks about fifty years old, and there is a wonderful vigor about him." He is also said to have "a voice like thunder" and the script later refers to him once as "the goat-man".
Despite being consistently named Lucien in the script, he at first introduces himself to the Enterprise crew as Baal, though this line of dialogue is not in the episode's final version. Another ultimately-unused line, spoken by Lucien during the trial, establishes that he visited Babylonia, Mesopotamia, and Greece while on Earth.
Lucien's character design appears very similar to that of a satyr boy who that appears in "The Magicks of Megas-Tu". Also, the novelization of that episode (which was published in Star Trek Log 3 and repeatedly refers to Lucien to as "the goat-man") refers to the satyr child (who is referred to as a "satyr" only in the episode's script) as "a small goat-boy," indirectly acknowledging the similarities between their looks.