There’s no question that William Shakespeare was a real person who was active in the theater during the reigns of Elizabeth and James. The only debate here is whether he actually wrote the plays attributed to him, or if he was just an actor who allowed someone else to publish them under his name.
And speaking of poets of questionable provenance, there almost certainly wasn’t ever a real Homer - the Iliad and the Odyssey were compiled by multiple unknown poets over the course of many years.
This guy is no longer well known, but in the 14th century there was a book published called The Travels of Sir John Mandeville which was an extremely popular and successful account of the author’s supposed travels to the Holy Land.
Despite becoming a best-selling Medieval author, it’s now believed that Sir John Mandeville himself didn’t actually exist. The author - whoever he was - probably got as far as the Mediterranean, and then made up the rest out of a vividly fertile imagination.
It’s a very entertaining book. Rather nuts, in places, but definitely entertaining.
Why would you assume that? Do you assume Noah was some guy who built a really big boat?
Both things can be true. There can be an oral tradition (or multiples of) passed down through the generations, compiled by multiple unknown poets, that a poet named Homer then moulds and embellishes, with his Shakespeare-like literary genius, into a single epic poem that’s so good it becomes a definitive Greek cultural work and is passed down, word by word, by future poets through history.
Yeah; but his real name was Utnapishtim, and he didn’t carry more than his family and livestock on his reed raft. And he never reached Mount Ararat. 
I always thought the flood story was perfectly plausible if Noah had scaled down the boat somewhat and only brought one animal of every kind on the ark.
If the Steve whose existence you have demonstrated is the person who is supposed to have been the son of God and to have levitated a football stadium, as opposed to being an entirely unrelated person who by coincidence shares a name and certain characteristics with a wholly mythical Steve, then, yes, you have proved his existence.
In the same way, it’s not necessary to prove that Alexander the Great was conceived by a thunderbolt in order to prove the existence of Alexander the Great.
For the record, I certainly didn’t think that you actually thought he was. 
BTW: Another element to the discussion is the fact that even well-documented historical figures will have plenty of legends, tall tales and anecdotes surrounding them. See: Washington and the cherry tree.
There’s a famous anecdote about Alexander’s encounter with Diogenes of Sinope (the philosopher who lived in a barrel, masturbated in public, and used to post on this board). Alexander wanted to grant a wish for Diogenes. The philosopher replied: “Stand out of my light.” That is, Alexander was blocking the sunlight for Diogenes, who was sunbathing, and the only thing Diogenes asked was for him to move a bit out of the way.
That’s pretty cheeky, but Alexander admired the response, and proclaimed: “Were I not Alexander, I would want to be Diogenes.” (I’ve heard one version where this in turn then prompted Diogenes to quip: “Were I not Diogenes, I would *also *want to be Diogenes.” He was a funny dude.)
Alexander was real, Diogenes was real, and this anecdote is always repeated when either of them comes up in discussion. It tells us a lot about the personalities of both. But historians doubt that the meeting happened. No two versions of the anecdote seem to agree on the details, and it’s most likely just a just a good story that has grown (and is still growing) in the telling.
It doesn’t mean that we will or should stop telling it at every opportunity. It’s a good story. And even if it’s fictional, the fictionalization itself has become historical, if that even makes any sense. If you put this encounter in a biopic about Alexander, I won’t be upset in the slightest, and I’m usually the first one to cry foul when it comes to historical inaccuracy. Whatever this anecdote is, “historically inaccurate” just doesn’t feel like the right description for it.
Somewhat similarly, I’ve read a biography of Caligula without any of the juicy gossip, and it seemed vaguely pointless. Suetonius is just better.
One thing most scholars agree on, I believe, is that if Arthur existed at all, he was NOT a King. As “Dark” as the centuries after the end of Roman power in Briton were, there are some records, and they leave no room for a superfluous major King.
Moreover, Nennius’ Historia Brittonum, which was written centuries after the alleged battles it describes, is not taken seriously IIRC, and many of the place names it mentions are unrecognizable.
There is one “Arthur” who has been hypothesized for centuries and who is undergoing a recent revival. Artúr mac Áedáin may have been a commander of knights in the late 6th century with a Round Table at Stirling. This Arthur’s father was a Scots King, ruling to the north of the Brythonic-speaking domains, but who was allied and intermarried with Britons. This hypothesis would solve several problems; there is room for unknown place-names in the poorly documented North, especially since the Britons were eventually pushed out; and would explain why both Scots and Welsh treat Arthur as their folk hero. But the divergence from the traditional places, dates and manners of the legend is severe.
Nxxt you’re going to tell me that Babe the Blue Ox doesn’t exist either. Geeze you’re just sucking all the fond memories of enormous RGB (0, 0, 255) castrated bullocks out of my childhood.
But this is petitio principii. You are assuming the existence of a real unique historical person who corresponds to the person in the myth (whether or not the supernatural elements are real or imagined). If the character is invented, or is a composite, there would be no such correspondence.
It seems to me that “existence” is not a well defined notion in many cases. There will usually have been real people who possessed at least some subset of the claimed characteristics of the mythical figure, but not all. What’s the threshold for claiming that a real identifiable historical individual was the mythical person?
ETA: for example, in the situation a couple of posts above: is it at all reasonable to claim that King Arthur did exist, but was not a king? I assume that Arthur was not such an uncommon name at the time.
Of course he existed! Babe too! There’s lots of statues of him here in Minnesota!
It broke my sixth-grader heart to look up Paul Bunyan in the encyclopedia. Even my elderly teacher that year thought he was real and that’s why she had me look it up.
There are people who think John Henry actually existed? I’ve always assumed he was as legendary as Paul Bunyan (though not as phantastic).
Colonel Tomb: Ace pilot of the North Vietnamese Airforce. Supposed to have shot down 13 US aircraft while flying a MiG-17 (number 3020) and brought down by USN fighter-pilots after a fierce dogfight.
Almost certainly never existed in the form of a single pilot:
Look at the Wiki link, several people try to establish his identity. I’m sure there was at least one railroad worker of incredible strength and endurance that spawned legends, and possibly one named John Henry according to the Wiki. The contest between any of these men and a steam drill is less likely. I could see the new steam drill showing up at the work site one day and some strong laborer outperforming it for a while until the operators got things running smoothly. The idea of a man beating the machine but dying in the effort is a little too pat.
No, I’m not assuming it. You’re postulating that the existence of an actual Steve is established. I’m saying that if actual Steve is the person who is supposed to have had supernatural characteristics, then the existence of that person is established (but the fact that he had supernatural characteristics is not). When I say explicitly that this is conditional on a certain thing, I am not assuming that thing.
This is a matter for historical investigation. We have to ask ourselves, how did the story of levitating Steve arise, and who was it told about? Was the story simply make up out of whole cloth about a fictional or imaginary person, so that the existence of an actual Steve who shares some characteristics with the subject of the myth is a mere coincidence? If that’s the case, pointing to actual Steve does not demonstrate the existence of story Steve; they are different people. But if this story was originally told about actual Steve and, if you have demonstrated the existence of actual Steve, you have also demonstrated the existence of story Steve.
Of course, the nature of historical investigation is that we may be uncertain as to whether the story was originally told about actual Steve or entirely imaginary Steve. Proving the existence of actual Steve, living at the right time and in the right place, makes it more plausible or more possible that the story relates to actual Steve, but it doesn’t make it certain. The more characteristics actual Steve shares with story Steve (and the more unusual/distinctive those characteristics are) the more likely it is that the story refers to actual Steve.
What could certainly happen is that a story is originally told about, say, the god Apollo, but at a later date is told about, say, Alexander the Great. Obviously, the subject of the story about Alexander the Great was a real person and did exist, and his existence is in principle demonstrable. So can we demonstrate that the subject of this story is a real person? Yes, in principle. But that’s not at all the same thing as demonstrating that the story is true.
In a similar vein, there is (as far as I know) absolutely no documentary evidence for the existence of German snipers Erwin Konig and Hans Thorvald; against whom legendary Russian sniper Vasily Zaitsev allegedly fought duels with in Stalingrad during WWII.
Given the Nazis were fastidious record keepers, and no-one in Germany that I know of has come forward to say “My great-grandfather [or other relation] Erwin or Hans was a sniper and got sent to Stalingrad and never came back” I’d say it’s likely they were either made up as part of a Soviet propaganda exercise, or else were names applied to other German snipers whom Zaitsev might have killed.
Whatever the historical origins and development of the story, if the only remarkable thing about mythical “Steve” is his claimed supernatural abilities, and all his other characteristics are unremarkable and were circumstantially almost certainly held by numerous people in the society of the time, then it’s pretty much an empty and meaningless statement to say that mythical Steve “really existed”, but just wasn’t supernatural.
“Steve” is a rather extreme example in that regard, but no more so than (say) Romulus and Remus, so far as I’m aware. Do they have any distinguishing characteristics that are not supernatural? If we could show that a couple of real people were around who played a hand in founding Rome in a rather more conventional fashion, and had similar names, could we reasonably claim that Romulus and Remus “really existed” as historical figures? It seems to me that we have shown that two other somewhat interesting people existed, but these people were clearly not Romulus and Remus.
It seems to me that it’s often the case that the historicity of some figure is something that cannot, even in principle, have a definitive objective answer, yet people treat it as though it does. There’s no objective answer to the question of what proportion of the mythical properties a real historic person must be shown to have possessed in order to claim that the mythical person was “real”?
If during the time of his life this person was considered the person of legend we may as well accept him as real no matter what inaccuracies occur in the legends. The existence of this person doesn’t validate the legend, nor does the legend prove his existence, only the historical evidence can prove his existence and his association with the legend.