Where did the Ancient writer of Revelation, ostensibly named ‘John’, but not necessarily the Apostle John, come to know about ‘dragons’?........................
By the way, if you see a painting with a horsed lancer stabbing a dragon, and there are many, that is George, not Michael.
That’s a fascinating question. If you rely on the KJV, the word rendered “dragon” comes up quite a bit in the OT. Newer translations, however, usually render these as “serpent” or “jackal” or something else that seems to fit the context better. (e.g. Isaiah 34:13
One possibility that occurred to me was that, among other places in popular Jewish and Greek literature of his time, John probably was familiar with the story of Bel and the Dragon. This is a story that is not in the Protestant or Jewish canon of the Bible, but it has always been included in the Bibles of Catholic, Orthodox, Ethiopian, and other ancient churches as Daniel, chapter 14. It was included in the (2nd century BC) Greek Septuagint versions of the Old Testament which was used by the early Church (over 85% of OT citations in the NT are from the Septuagint) which John must have been familiar with.
Even if one does not consider the story canonical today, it should be considered at least an indication that stories of dragons in Jewish/early Christian circles were not unknown John and his contemporaries.