I dunno if you all had heard it but, But i think of Superman even though a fictional character, is in a lot of ways a modern messiah like figure. I have heard it said that Superman's story in some interesting ways mirror's that of the Story of Jesus's. Jor-el sending his only son to earth is like when God sent His son to earth. Superman was raised by two earthly parents same with Jesus being raised by Mary and Jospeh. Both of them using there values and teachings to help people, Both have arch-villians Superman's villian Lex and Jesus's villian is the devil. Both have died and have been brought back to life. These are what I have seen in both of them. I guess thats why Superman has reached all ages because of the similairities he has with Jesus.
He wasn't based on Jesus, there are TONS and TONS of characters from mythology that share the same basic story.