The Great Maw is the patron-deity of the Ogres that inhabit the Warhammer Fantasy universe, although the Great Maw is not entirely malevolent it is served by a species known for their brutality and insatible hunger: traits that the Great Maw seems to embody and champion.
Like many deities the Great Maw has no true form of its own but is represented by a huge gaping mouth, inhuman and circular, with numerous jagged teeth. Ogre culture revolves around eating, and as such the priest of the Great Maw are butchers, slaughtermasters, and cooks. It must be noted though that the food is entirely animal, with no vegetable matter whatsoever (making Ogres entirely carnivorous). Their religious holidays are supervised by the ogre butchers, and consist (mainly, and some times solely) of gigantic banquets and pit fights. Skrag the Slaughterer is the prophet of the Great Maw and thus can be considered one of its greatest champions.
The origin of the Great Maw goes back quite some time... 2,750 years before the Empire of Man's founding, to be precise. The Ogres of those days lived in lands that bordered the oriental empire of Cathay. In those days, the Ogres were fearless, feasting whenever, wherever and on whomever they chose, without concern for repercussions. Being simple-minded, they never considered the fact that somebody might want revenge... ultimately, this is what would decimate them.
What happened next has been debated about by scholars for years- some claim that the Ogres insulted the Dark Gods, others that the Celestial Wizards of Cathay attacked as vengeance for the losses of the many children of their empire. Regardless of belief, the end result was undeniable- a great meteor of warpstone (the largest ever seen) plummeted from the skies and landed straight into the heart of the Ogres, killing off two-thirds of the Ogres' population and creating a giant, pulsing maw lined with jagged teeth where an impact crater should've been. For the first time, the Ogres have something to revere- and, by extension, something to fear.
The remaining Ogres fled west, fear gnawing at their hearts (though some refused to leave, becoming Yhetees- Yetis, in other words -in the warpstone-dusted mountains). To this day, the Ogres show respect to the Great Maw, because (as they so believe) "it must have been mighty indeed to devour so many [Ogres] in such a short time".