From what we see of Theo, he is a cowardly, timid Moon Person who grows stronger even over the course of his time in Muska Lacka. His time with Toan and Ungaga accounts for most of this shift.
At first, he refuses to go with Toan, but the Mayor of Brownboo Village insists on it, since being the Mayor is very difficult work, to which Theo retorts that there is nothing to do as Mayor. He still guides them there, much against his will. He is rather shocked but not at all surprised to find that Muska Lacka, too, has been destroyed by the Dark Genie. What does surprise him, however, is that the great and legendary Ungaga of the Sand Tribe has lost his will to fight after failing to protect the village from the wrath of the Genie. Partly because he doesn't want to go into the Sun and Moon Temple with Toan, Theo stays with Ungaga in attempt to cheer him up, being quite a fan of Ungaga from what he has heard of him.
Theo compares Ungaga to Toan during his talk with him, saying that they are both strong warriors, but that Toan doesn't give up, and that's where his will comes from. Ungaga takes this the exact wrong way, saying that Toan is therefore strong, while he is weak. After a while of trying and failing to cheer the spearman up, it is well into the night. A shooting star flies across the sky, causing Theo to stand up and shout the phrase "Lucky Cookie Zucchini!" into the air, apparently for good luck. Surprisingly, this seems to cheer Ungaga up more than Theo's other attempts, as when we next see Ungaga upon completion of the Three Sisters' House, he has regained his confidence and is ready to help Toan in his fight. Theo is outside when Toan exits the house, and wishes Toan well once more before vanishing back to Brownboo village.
When Toan activates the Moon Ship and begins his ascent to the moon, we see a Moon Person in Brownboo Village, likely Theo, watch from a high cliff. He takes off his hood, revealing for the one and only time in the first game that the Moon People have the appearance of rabbits underneath their hoods.