Short answers, pulled from the story.
A deity, or god, is a supernatural being considered to have authority over some aspect of the universe or of life, with many also regarded as sacred and worthy of worship. The Oxford Dictionary of English defines deity as a god or goddess, or anything revered as divine. C. Scott Littleton describes a deity as a being with powers greater than ordinary humans who interacts with people in ways that carry them to new levels of consciousness.
The English word deity derives from Old French deite and the Latin deitatem, meaning divine nature, a term coined by Augustine of Hippo from deus, meaning god. Deus connects through a common Proto-Indo-European origin to the root deiwos, which is tied to the idea of shining and also yields the ancient Indian word Deva.
Monotheism is the belief that only one deity exists, polytheism is the belief in and worship of multiple deities usually gathered into a pantheon, and henotheism accepts more than one deity while treating them all as equivalent aspects of the same highest divine principle. Monolatry holds that many deities exist but only one may be validly worshipped.
Egyptologist James P. Allen estimates that more than 1,400 deities are named in Egyptian texts, while Christian Leitz offers an estimate of thousands upon thousands. Around 200 deities are prominent in the Pyramid texts and ancient temples, many of them zoomorphic, including Min, Neith, Anubis, Horus, Isis, Ra, and Thoth.
The most important deities in the Greek pantheon were the Twelve Olympians: Zeus, Hera, Poseidon, Athena, Apollo, Artemis, Aphrodite, Hermes, Demeter, Dionysus, Hephaestus, and Ares. The Roman pantheon syncretized many of these with figures such as Venus, Mars, Minerva, Juno, and Jupiter, alongside non-Greek deities like Janus, Fortuna, and Quirinus.
Democritus argued that the concept of deities arose when humans observed natural phenomena such as lightning, solar eclipses, and the changing of the seasons. Modern thinkers point to an overactive agency-detection system, a tendency to think teleologically, and, as Matt Rossano proposes, the use of God-concepts to enforce morality and build cooperative communities. Children are naturally inclined to believe in gods, spirits, and demons even without religious instruction.