This page is typical of the many that debunk the Jesus myth as nothing more than a conglomeration of pre-existing deities. Whilst I've no doubt that there is truth in this notion, the link between Mithras and Jesus seems to be tenuous at best.
Now, I'm no scholar of religious history, you shouldn't take my word as gospel. I know of at least two esteemed readers who posess the means to, or knowledge of, this matter way in excess of mine. I'd be interested to hear their points of view.
So, on to the business of debunking the debunked;
Mithras was born of a virgin on December 25th in a cave, and his birth was attended by shepherds.
Falseish. Mithras was born out of a rock. His 'birth' was witnessed by shepherds though. Apparently they dragged him from the rock. I suppose then, the rock / virgin metaphor can be used, though it seems a bit of an imaginative leap to be took seriously I think. It's conceivable that Mithras would have left a 'cave' behind perhaps.
Mithras was worshipped as a sun god. It stands to reason then, that a festival to celebrate him would be close to the winter equinox. Mithras was far from alone in this respect. There are myriad sun gods around the world being worshipped right now. It's likely that Christmas did subsume these 'pagan' festivals, though to attribute this specifically to Mithras again seems too much of a leap of faith for me.
He was considered a great traveling teacher and master.
Erm, find me a religious leader who wasn't? This is by no means a spooky coincidence.
He had 12 companions or disciples.
Mithras had only two companions - Cautes and Cautopatres. Nowhere are the ten missing disciples mentioned directly, either in writings or imagery.
Mithra's followers were promised immortality.
Perhaps this is valid. Though again, hardly a spooky coincidence. Notions of immortality / heaven / reincarnation are a common facet of most religions.
"As one Mithraic scholar put it, Mithraism "surely offered its initiates deliverance from some awful fate to which all other men were doomed, and a privileged passage to some ultimate state of well-being." [MS.470] Why is this a good guess? Not because Mithraism borrowed from Christianity, or Christianity borrowed from Mithraism, or anyone borrowed from anyone, but because if you don't promise your adherents something that secures their eternity, you may as well give up running a religion and go and sell timeshares in Alaska!"
He performed miracles.
Perhaps he did, I can find no direct examples of them however. Besides, miracle wrangling is a prerequisite to godhood surely?
As the "great bull of the Sun," Mithra sacrificed himself for world peace.
Mithra did not "sacrifice himself" in the sense that he died; he was not the "great bull of the Sun", but rather, he killed the bull. Mithra could only be said to have "sacrificed himself" in the sense that he went out and took a risk to do a heroic deed
Anyway, I think I've made my point. If you want to find out more, you could do no worse than starting here. Of course there's little doubt that the Christian myth took inspiration from many sources. But we should be cautious when simple explanations like the Mithras - Jesus are spouted. However attractive they are.
I'll leave you with this Steven Fry clip from the superb QI.