battlestar galactica - Who are the two people that look like Baltar and 6 at the end of the series?

In the last episodes of BSG we see Baltar and 6 walking in our present days and observing.

Who are they? Why do they look exactly like the original two? And why do they seem to know the "real story" of humanity as opposed to anyone else?

Quotes from Daybreak Part 2

Virtual Six: Commercialism, decadence, technology run amok. Remind you of anything?
Virtual Baltar: Take your pick. Kobol. Earth... the real Earth, before this one. Caprica before the fall.
Virtual Six: All of this has happened before.
Virtual Baltar: But the question remains, does all of this have to happen again?
Virtual Six: This time I bet no.
Virtual Baltar: [Stops] You know, I've never known you to play the optimist. Why the change of heart?
Virtual Six: Mathematics. Law of averages. Let a complex system repeat itself long enough and eventually something surprising might occur. That, too, is in God's plan.

Virtual Baltar: [Serious] You know it doesn't like that name.
[Six gives Baltar a defiant look] Silly me. Silly, silly me.
[The two walk arm-in-arm off into the streets.]

Answer

According to the series co-creator Ron Moore, they are the "Head Six" and "Head Baltar", agents of a higher power. They know the "real story" of humanity (and Cylons) because they are eternal, and were around for the previous cycles:

In the last scene, are “Six” and “Baltar” angels or demons?

Moore: I think they’re both. We never try to name exactly what the “Head” characters are—we called them “Head Baltar” and “Head Six” all throughout the show, internally. We never really looked at them as angels or demons because they seemed to periodically say evil things and good things, they tended to save people and they tended to damn people. There was this sense that they worked in service of something else. You could say “a higher power” or you could say “another power,” [but] they were in service to something else that was guiding and helping, sometimes obstructing, and sometimes tempting the people on the show. The idea at the very end was that whatever they are in service to continues and is eternal and is always around. And they too are still around…and with all of us who are the children of Hera. They continue to walk among us and watch, and at some point they may or may not intercede at a key moment.