Rat Culture & Religion
Wild Rats have a very simple belief structure.  Specific religions vary from one colony to the next, and are determined in large part by the whims of the alpha rat.  Nevertheless, most wild rats spend very little time worrying about religion.  
Domestic rats traditionally worshiped humans ("The Great Ones") as bringers of sustenance and great, omnipotent protectors.  Now that humans are gone, some rats have begun to change their mind about the role of The Great Ones.  Others still cling to those beliefs and believe that the humans will return one day to bring them to salvation.  
The Spirit Realm:When rats die, their souls enter the spirit realm.  This world is limitless, where there is a constant abundance of food and no predators.  All the rats from the beginning of time live here peacefully, and watch living rats through a thin grey mist that separates the spirit realm from reality.  
All rats, domestic and wild, believe in a collective repository of memory.  This is how they account for all instinctual knowledge, and they believe that by praying to the spirits of the dead that they will be able to learn skills.  Essentially, rats believe that everything any rat has ever known can be learned if you are able to speak with the right spirit.  
The only rats that can communicate directly with the spirits are Usoothe.  These seers are gifted with the ability to "see further" than others and look beyond the grey mist.  All rats will pray to the spirits, however, and may receive guidance during times of extreme duress.  
For example, a rat caught in a flood may pray to the spirits to teach her how to swim.  Even though she has never seen water before, the spirits of those rats who swum from China to Norway are able to show her how to do it.  Of course, skeptics would argue that this is just instinct...but there are very few skeptical rats.  
Considering the sheer number of rats that have ever existed, it's reasonable to expect that the spirits have a 
lot of knowledge.  
RanksWhile all colonies will have their own ranks, some of the more standard across all colonies are: 
Alpha:  Known by various names in different colonies, the alpha is the head rat.  Peaceful rats will call him the Usim-li or "Good burrow-keeper", whereas war-faring rats might call him Ukeshu or "Lord who bites enemies".  No matter what the name, an alpha's title will always start with "U", which denotes respect.  
Traditionally, alphas are males.  They often take a harem of females, although there may be one favorite female in the bunch.  His sons and other males in the colony would be allowed their own harems, but the alpha male would always have first choice of breeding and could chase the other rats away at any time.  
More recently, other colony constructions have become possible.  
Usoothe:  Highly revered as religious icons by the other rats, the Usoothe are seers.  They are gifted with the ability to speak with the spirits, and this enables them to know things that normal rats do not.  They may be able to speak with other animals or read Human writing.  They might be able to catch glimpses of the future or read the thoughts of other rats.  Usoothe are very rare and are well-guarded because of their rarity.  The trait is not genetic, and seems to appear randomly, developing during adolescence.  
Allaysi:  Hunters and scouts, these rats are young, nimble, and fearless.  Usually some of the smartest and quickest rats in the colony, they are the rats that scout out new food sources, infiltrate enemy colonies, and look for new places to live.  Allaysi are usually female, but can often be young males as well.  
Keshu:  Warriors and guards, these are large-bodied, tough rats.  Usually male, but super-tough females are able to fill this role as well.  They are more likely to become alphas than any other type of rat, as they are the most likely to challenge the alpha for the position.  
Nosobo:  Healers and nursemaids.  The nosobo are reputed to have a nearly magical healing quality, but it's never been completely proven that there's anything supernatural about their abilities. They are usually gentle, soft-spoken rats.