If we believe the Bible, then the question doesn’t even need to be addressed: of course he was for real. But there are other questions we can ask, whose answers can further illuminate the Bible for us.
Pictured above is a set of Mycenean body armor from Greece, circa 1200 B.C.: this and others like it can be seen in museums. Goliath probably had similar equipment–only his would have been new, well cared-for, and would have shone brightly–one might easily say alarmingly–with reflected sunlight.
Was Goliath a giant? Earlier Biblical texts, such as the Dead Sea scrolls, give his height as “four cubits and a span,” or about six feet nine inches. The NBA is full of guys that tall or taller; but back in the Bronze Age, six-foot-nine would have been much taller than the average full-grown man. Our King James Bible says Goliath was “six cubits and a span,” or nine feet nine inches tall: but that comes from the later Masoretic Texts and may be a scribal error.
Either way, Goliath was probably by far the biggest man in either army; and the armor he wore would have made him look even bigger. Ancient armor had two purposes, not just one: to protect the wearer, and to intimidate his foes. Goliath in new armor would have intimidated most people. Indeed, he intimidated everyone but David.
There’s a lot that we don’t know about the Philistines, including where they originally came from. Their artifacts suggest the islands of the Aegean Sea, or Crete, or the southeastern coast of Asia Minor. The ancient Egyptians called them “Peleset,” one of the Sea Peoples blamed for wrecking Mediterranean civilizations at the end of the Late Bronze Age. We don’t know what the Philistines called themselves.
The Greeks of the Mycenean civilization, the ones who fought the Trojan War, had a custom of settling matters between armies by single combat between each army’s chosen champion: Menelaus vs. Paris, Ajax vs. Hector, in The Iliad (in which neither of those two combats was allowed to go to a finish). Goliath challenges Israel’s army to send out a champion to fight him. His procedure is the same as what we see in Homer–and suggestive of authenticity.
When David killed Goliath, the Philistines panicked and fled. The strictest rules of Bronze Age military etiquette–which were observed by virtually no one–called for the Philistine army to leave off its operations and peacefully retire. But because they ran, the Israelites chased them back to Philistia. We doubt the Greeks would have sailed home from Troy if Paris had succeeded in killing Menelaus… although the rules said they should have.
The Bible provides us with many glimpses into long-lost epochs of history, many of which wind up being further illustrated by archaeological discoveries.
There is nothing in the story of David and Goliath to prevent a reasonable person from believing it.