Final answer:
Montezuma believed that Quetzalcoatl, the 'feathered serpent' and a prominent Aztec deity, might have come to reclaim his throne during the arrival of the Spanish conquistadors.
Step-by-step explanation:
The god that Montezuma believed might have come to reclaim his throne is Quetzalcoatl, the "feathered serpent" and Aztec god of wind, dawn, merchants, and knowledge. Montezuma II, the ruler of the Aztec Empire at the time of the Spanish conquest, associated the arrival of the conqueror Hernán Cortés with the prophesied return of Quetzalcoatl. This belief was rooted in Aztec religious views that anticipated the arrival of Quetzalcoatl at an undisclosed time to reclaim his place. When Cortés arrived, Montezuma is reported to have said, "We have always held that those who are descended from [Quetzalcoatl] would come and conquer this land and take us as his vassals."