Have you heard of Superman? Maybe you've read a comic book or two featuring him. Maybe you've seen at least one of the films in which he was depicted. And if not, you've probably encountered hundreds if not thousands of cultural references to him during your life. So yeah, it is probably safe to assume that you've heard of him.
It wouldn't make much sense if I were to claim that the fact that you've heard of him means that he's real, would it? One hardly follows from the other. And if I were to insist that the fact that most people have probably heard of Superman was evidence that he must be a real person, that wouldn't be any more convincing, would it? That a fictional character is popular does not make him or her any less fictional.
This all seems fairly obvious, doesn't it? I'd like to say that most people can easily grasp this and move on. I cannot do so, however, because I have heard this "argument" from Christians more times than I can count as they attempt to convince others that the Jesus character depicted in their bible was a real historical person or worse - that he is still around in some way that makes even less sense. The number of people who have heard of Jesus is no more relevant to his reality as was the number of people who have heard of Superman. The popularity of Jesus does not make him real.
But look at how influential Jesus-belief has been! I'll certainly grant you that the concept of Jesus has been far more influential and for a much longer period of time than the concept of Superman; however, we've already agreed that the fact that the Superman concept has been influential does not mean that he is (or was) real. The same is true for Jesus. Perhaps there is evidence that a historical Jesus existed or even that some sort of supernatural Jesus exists now, but the number of people who believe it is not valid evidence. And neither is the bible.
