It’s strange but true: Just about every aspect of Our Lord’s life and character is foreshadowed, in some way, in the myths and legends of pre-Christian paganism. This fact was very obvious to people of the 2nd and 3rd centuries. So obvious, in fact, that the pagans often used it as an argument against the Faith! The Christians, after all, spoke of Jesus as a real man, who lived in a certain city, in a certain country, not much more than one long lifetime earlier. And yet it seemed clear to the pagans, that their Christ was just one more example of the typical mythological avatar—just another Icarus or Heracles. Just one more “Corn King”—who dies and rises again, bearing much fruit. And Christ’s teachings seemed to them to echo, at times, the ethics of Zeno or Epictetus.
Well, this is where St. Justin came in…
There's also a quote Rod mentions from the young C.S. Lewis which shall be shockingly familiar to those of you have had any dealings with "young atheists:"
“You know, I think, that I believe in no religion. There is absolutely no proof for any of them, and from a philosophical standpoint Christianity is not even the best. All religions, that is, all mythologies to give them their proper name, are merely man's own invention‑Christ as much as Loki. Primitive man found himself surrounded by all sorts of terrible things he didn't understand...thus religion, that is to say mythology grew up.”