Herald of Opera asks:

It just occurred to me… with a name like “Great Thinker” and our primary source being the Atlantis guy talking him up, how sure are we that Socrates actually existed?

So… we’re pretty sure he existed, because Plato is our main source but not the only one who talks about him.  After his death,  we also have philosophical texts written about him by Xenophon, another of his students.  More importantly, while he was alive and long before Plato started writing philosophy (possibly even before Plato was born), Socrates was parodied by Aristophanes in his comedy, the Clouds, so it’s pretty definite that he wasn’t just completely made up in hindsight by Plato.  There are comments in some of Plato’s dialogues suggesting that he was trying to undo the play’s effect on Socrates’ reputation.  Also, although the events of the dialogues are fictionalised (with the exception of the Apology and maybe parts of the Phaedo), almost all the characters in them are real people, attested in other historical texts like Thucydides’ Peloponnesian War or Xenophon’s Hellenica, whose positions in the philosophical debates reflect their real reputations and life stories.  It would be… weird, put it that way, for Plato to construct such an elaborate fiction of a guy who never existed, tie it into the lives of so many other people, many of whom were Plato’s own friends, acquaintances and relatives (several of them dead by the time Plato started writing, most of them not peacefully), and give him a backstory deeply woven into the traumatic events of the Peloponnesian War.  If nothing else, I suspect it would have been in very bad taste.

On the other hand was Socrates exactly the person we see in the Apology, the Phaedo, the Gorgias, and so on?  That’s… well, that’s one of the ongoing debates in the scholarship on Plato’s works.  Plato’s Socrates and Xenophon’s Socrates are not quite the same person; Xenophon’s Socrates has less of the trademark pain-in-the-ass conversational style and doesn’t share all of the same philosophical ideas.  Some of that is probably just differences in their respective memories of him as a person, but they are also both developing Socrates as a “character” to make their points and tell their stories.  A lot of the ideas put into Socrates’ mouth by the dialogues are probably Plato’s.  I doubt, for instance, that the historical Socrates believed in the doctrine of Forms, as expressed in the Republic, the Timaeus and so on, or that he ever wanted to create an ideal city ruled by philosophers (which is clearly an ambition related closely to Plato’s own life experiences, his time in Syracuse and his consciousness of – and, in my opinion, guilt over – his own failure with Dionysius II).  But he must have had philosophical ideas, since Plato and Xenophon both cite him as a huge influence on their lives and beliefs.  There’s actually a pretty substantial body of scholarship that tries to divide Plato’s works into “early” ones, like the Apology and the Gorgias, that are heavily influenced by the ideas and personality of the historical Socrates, and “late” ones, like the Timaeus, where Plato is expressing his own ideas and Socrates is more of an artificial character (or absent altogether, as in the Laws).  Of course, the trouble with these arguments is that they sort of rely on our own preconceptions about what Socrates’ real philosophical beliefs were (because there’s very little direct evidence for the date of any of the dialogues), and the whole scheme can become, frankly, circular.  I’ve had the impression that a lot of Plato scholars these days take it all with a grain of salt, for precisely that reason. I think it would be fair to say that, although Socrates was certainly a real person and certainly known for philosophy, no one really knows for sure what he was like, or what he believed.

Not sure what you mean about his name or where you’re getting “great thinker” from (that would be… I don’t know, Megaphron or something); “Socrates” means something like “secure strength” (so- from the same root as the verb σώζω, to protect/save/secure, -crates of course from κράτος, strength/power).  There are a couple of other Greeks with the same name in the historical record, including a mercenary commander who would have been born well before Socrates became famous.  Names with the -crates suffix in general are also pretty common.  It’s not a particularly noteworthy or artificial-sounding name.