Ubtao, the Creator of Chult, the Father of Dinosaurs, Ubtao is worshipped by the Chultans as the creator and protector of Chult, he is described as a gigantic humanoid or enormous tyrannosaurus, and is believed to watch over the Chultans and guide them through the maze of life (and death.
The tabaxi believe that Ubtao created Chult, the jungles and the dinosaurs, and everything else on the peninsula. When Ubtao slept after this great act of creation he inadvertently caused Dendar the Night Serpent to crawl into existence, feeding off the nightmares of Ubtao.
Ubtao imprisoned the Night Serpent within a maze beneath the Peaks of Flame, but as penance for his carelessness he was tasked with guarding the Nightmare Gate (a set of huge iron doors in the Peaks of Flame that lead to Dendar’s Prison) for all eternity, and in return he would remain the unchallenged god of Chult and its people.
The Chultans believe that Ubtao created them and made the city of Mezro for them. He dwelt in Mezro for a time, teaching the Chultans about the Maze of Life (and Death) and how to recognise and navigate it, however, the Chultans tried to tame Ubtao and make him solve all life’s challenges.
Eventually Ubtao tired of the mundane problems of the Chultans, he created the Barae; his sworn protectors and guardians, and then vanished from Mezro forever, but his guiding hand remained to help steer the Chultans to walk the path of their own maze.
The Chultan mythology argues that Ubtao created Chult and everything in it, and that he guards the Nightmare Gate to stop Dendar the Night Serpent from devouring the entire world.
These myths only hold small grains of truth, for Ubtao did not create the Chultans, they arrived on Chult after journeying from a far off continent to the west of Faerun. Likewise Ubtao did not create the dinosaurs or Mezro, or the peninsula itself, but he does have a link to the reptilians and events on the peninsula and is tasked with protecting Chult.
Ubtao is in truth one of the supposed gods of the sarrukh of Mhairshaulk, his name representing a corruption of the draconic runes that spell out Varae. Ubtao, like the rest of his kindred godlings was born when Merrshaulk transformed himself into an anathema (calling himself the World Serpent), and consumed a variety of creatures native to Chult to try and combine them into new varieties of scalykind.
Merrshaulk succeeded in creating the naga, the yuan-ti, and a host of other part reptile, part other creations, but he eventually fragmented into enormous snakes, reptilian humanoid monsters, and other snake-like abominations. Varae/Ubtao was one of these creatures, Dendar was another, and unleashed upon Chult these quasi-deities began to fight for supremacy of Mhairshaulk.
Ultimately Merrshaulk asserted his dominance by using an even greater power source hidden beneath the Peaks of Flame. His meddling caused the sarrukh and the fragments of Merrshaulk (including Merrshaulk himself) to fall into a deep slumber. The yuan-ti servants inherited the empire of Mhairshaulk, and cared for the slumbering sarrukh and their gods in the sacred sites of Chult and the Mhair Jungle.
The arrival of the couatl to Chult would see the final imprisonment of all the wandering gods of the sarrukh (some of whom still plagued the jungles of Chult), and the collapse of the empire of Mhairshaulk under the continual assault of flights of dragons.
Varae sided with the couatl, recognising kindred in the children of Jazirian, and was rewarded with the guardianship of Chult.