Do we know if Socrates was a historical character or a literary device used by Plato?
If I'm remembering my philosophy classes correctly (and it's been a while since I was in that ancient philosophy class or wrote my senior thesis), then there is more historical evidence for Socrates than for many others from those ancient times. I believe there are contemporary writers, aside from Plato, who wrote about Socrates.
Socrates was real enough - his teachings and style were recognisably different from Plato's. None of Plato's (and Socrates' ) contemporaries challenged the account of his life, trial or other biographical details. You may as well ask if Plato was a literary device of Socrates.
Wikipedia gives some references that seem to verify the life of Socrates. For example, Socrates was a soldier during the Peloponnesian War and was mentioned by others as fulfilling that role nobly.
How could Plato have pulled off such a prank and not been exposed?
Like any ancient character or personage, there are varying schools of thought. Some, like for jesus are easier to show that there is no evidence. For Socrates, though, there is more evidence for him than for the king of jews. That said, there are those with credible arguments against. He is mentioned in at least three plays, which again may not be real proof..............etc. Anyway, here is a pretty good summary argument for him being real.
Very interesting... if Socrates was not a real man but a literary device created by Plato, then the teachings of Socrates are the teachings of Plato. This would increase Plato influence on the world by at least a factor of Socrates...Thereby creating the teachings of Platocrates