Storytellers have told tales of magic and monsters from time immemorial. The Greek myths are widely known, with a myriad of Gods and monsters.
The Norse myths have dragons, dwarves and spirits.
The Celtic cultures (in particular Irish) have giants, goblins, magical cauldrons and sorcery.
Less well-known mythologies have the same range of magic and monsters, whether it be Hawaiian or Aztec.
Why is there such a fascination with monsters and magic? The usual explanation is that these stories explain strangenesses and unknown phenomena that the ancient peoples did not understand, and that knowing, for example, that the Gods are responsible for lightning makes the thunderstorm less frightening.
I don't agree. There would be far easier ways to explain such things, and so many of the stories do not actually explain any natural phenomenon or landmark. No, my explanation is far simpler. People like having a sense of wonder. People like stories. Big, extraordinary, magical events and monsters are fun. They brighten up the lives of the readers or listeners. Nowadays we have television and films, but back in the distant past the best wide-screen surround-sound cinematic effects were created by storytellers. And fantasies make the best and most exciting stories.