I've always thought that the Mashiach is one. But I recently heard from a friend that there is Mashiach ben David and Mashiach Ben Yoseph. And that one will bring the jews from the diaspora and the other will reconstruct the Temple or something like that. I don't know the sources of this and I've never heard anything like this, but is this true in some way?
Well, according to our tradition, the term "Mashiach" describes the anointed monarch. So, we are waiting for the monarchy to be restored, with everything related - full independence and religion freedom(e.g. freedom from idolatry). In our sources it is said that IF we merit to get the glorious ruler - we'll get Mashiach ben David, but if we not - we will get Mashiach ben Yosef - e.g. the hidden one, like in Egypt. But any way if it will be Moshiach ben Yosef, afterwards will be Moshiach ben David for sure - as it is predicted by our prophets. So, we are waiting for the monarchy, but it could be established not necessarily straight ahead.