Kthonthus lived on a mountain, high above the clouds, with other dieties. He created Anuther Planet and loved it so much that he forbade anyone from leaving. However, a female diety from his mountain left and created a colony somewhere else, known as "Attalantea".
Even after belief in Kthonthus had died down, the moral beliefs originating in his religion remained, and so the people of Anuther Planet maintained a punishment for those who leave the planet. The first spaceship from Anuther Planet was also named after Kthonthus. (Lurline and the White Ravens of Oz)