A major part of some forms of the Jesus Myth Theory is the identification of the Egyptian god Osiris with the Greek god Dionysus. Why is this so important? Because in order to even get close to a parallel with Jesus, you need to combine their stories. We are not told much about Osiris’ birth, but Dionysus had supernatural elements to his birth (but still not a virgin birth). Dionysus was persecuted, but he was not killed. Osiris, however, was killed and later made ruler of the underworld (although still not a resurrection).
But where do mythicists get this identification of Osiris with Dionysus?
To be far, they are not just making this up. Herodotus identifies these two gods in his Histories. However, if you just heard that, you would get a misleading impression. It is not just these two gods who Herodotus identifies with each other. He identifies all of the Egyptian gods with Greek gods. In fact he speaks about various temples in Egypt dedicated to a variety of Greek gods. The problem is that if you travelled to Egypt, even back then, you would not find temples to Greek gods. There is also no reason to think that Egyptians in Herodotus’s day would have seen their gods as the same as the Greeks.
What is Herodotus doing?
We need to remember why Herodotus is writing his history. Although he goes off into a number of cultural descriptions, he is primarily describing the war between the Greeks and the Persians. There is as much more propaganda in his history than straight history. The Greeks respected the antiquity of the Egyptians. We might think of ancient Greece as old but it is modern compared to Egypt. By connecting the Greek gods to the Egyptian gods, he is elevating the glory of Greece and their religion. Not only this, the Egyptians had revolted against Persia around the same time as the conflict between Greece and Persia.
The truth is that the gods of Greece and the gods of Egypt are very different. The story of Osiris is very different from the story of Dionysus. This is not like the identification of the Greek Artemis with the Roman Minerva or the Greek Hermes with the Roman Mercury. Osiris was a god of the underworld, while Dionysus was the god of wine and revelry. You can’t get any more different than that. To take pieces of Osiris’ story and mix it with pieces of Dionysus’ story is to disrespect both myths. Even Herodotus, for all his errors, didn’t do that.