Take the basic creation myth of the ancient Greeks, mix in a little modern cosmology, darken the origins/character of the creator, add a dash of female empowerment to his betrayal, and you've got how the Republic's Church of Man (or CHoM for a wink to Herbert fans) thinks that the universe came to exist. Which is to say that they think all of creation was screwed (quite literally) from the beginning. No, they're not a very happy people. :)
Of course the Colserans will only laugh and jeer at this myth. But we can develop their beliefs (such as they are) later.
Next up is the myth of the creation of men (including the Colser), which will be presented as another aberration stemming from betrayal. As the Republic exists at least 10,000 years in our future, expect the history of our time (a pivotal moment) to be um... biblically fanciful. :)
Don't worry, there won't be more than 3-4 pages of this stuff. But I think it's important to set the tone of the game's fluff right at the beginning of the book. We're a game made for adults, with adult (but not pornographic) themes. Think early Heinlein or Azimov without the graphic sex.