GORK IS BEZT AT KRUMMPIN'ND BASHIN WAAAAAAAAGH!!!
- The Words of Gork summing up Ork Kulture
Gork is one of the two Ork gods, the god of cunning brutality. He is the more brutal but cunning out of the twins, while Mork is the more cunning but brutal. The core "difference" between them is that Mork will hit you when you aren't looking, while Gork will hit you harder when you are.
Prior to 7th edition, Orks had no idea which god was Gork and which god was Mork (and debates were just another excuse to fight each other). This was eventually dropped because it was super awkward to write. Most likely, the Prophet of Gork and Mork laid down his head-canon, and the other Orks figured he was big enough to close the matter.
Gork, as noted, is the Ork god for sheer might and power. Some may debate that the ork Gods can compete with the Chaos Gods when talking about cunningness or power, but there is no way of knowing for sure. As the Warp's nature is ever-changing and spontaneous, the might of a certain god is never set in place. Although, there is a fact that each race's feelings are represented by an entity in the Warp and as the ork population and crusades grow in number, so does the might of Gork and Mork. In the long run, in a sense, he could arguably be one of the most powerful entities in the warp along with his twin Mork and the Chaos Gods. Unlike his twin, Gork favors (and in turn is often favored by) the likes of Warbosses and Nobz as well as countless other Orks due to his manifestation of the Ork's prime brutality and CQC fighting. Due to this, Gork may be more physically powerful than Mork but is less intellectually competent and cunning as a result, creating a balance of power between the twins.
From what can be determined, given what little (if any) history is available on the Orks, both Gork and Mork came into existence upon the Orks' creation when they inadvertently started channeling their essence (and wanton violence) into their gestalt field, similar to that of the Eldar; however the Orks' gods often like to get a bit more 'personal' with their subjects i.e. will offer cosmic aid to whoever is chanting their names long enough and if they decide they are worthy enough of their aid; if they are considered worthy, then woe to any forces opposing the tsunami of green people.]] Although they are both idolized upon, the Orks often have no idea who they are directly praying to resulting in much lulz if a Weirdboy praying for Gork's space foot to crush the enemy summons Mork instead, who makes his head explode for mistaking their identities (not that they care THAT much).
The only distinction that can be made between the two is that Gork is the more favored of the two gods for the more common greenskins, as he is the manifestation of power and might for the Orks, while Mork is more favored towards Orks that possess a sheer level of intellect and cunning such as BigMeks, Gretchins, Flashgitz and other Oddboyz. Whatever is the case, both are rumored to be more powerful than Khorne, due to the sheer psychic might of the Orks, and may actually have the power to snap Khorne like some sissy daemonette.
Mirroring the Orks as a faction themselves, Gork and Mork united could probably overpower any other god. Also much like the Ork race, they fight each between themselves as much as external threats, much to the galaxy's relief. Fundamentally, this is the reason for the Orks to venerate twin gods. Though mild distinctions can be drawn, in practice Gork and Mork are identical. The reason there must be two is that Orks prize the glory of combat above all things. Why have two gods where one would suffice? So they can fight.
Although no one has the faintest idea on what these twin gods may truly look like, they can at least be interpreted through the various designs of the BigMek's Stompas and Gargants, which are noted to be effigies of the two gods.
On the TabletopEdit
A classic magic spell for the Orcs in WFB is the Foot of Gork, where the Orcs use their magic to manifest Gork's massive foot whereupon he uses his mighty size to stomp whatever unlucky git is in the way flat into the mud. It is rendered in all its awesome glory in Total War: Warhammer.
The Foot of Gork also has an on-again-off-again relationship with 40k. Sometimes it's a normal Weirdboy spell sometimes it's rendered Apocalypse only, sometimes the writers think their army bright red Mad Max rovers with flamethrower guitars filled with fungus football hooligans is too serious for the magic spell about stomping on people. Luckily that last phase doesn't last long. In 8th edition the Foot of Gork has been renamed to Da Krunch, but the fluff paragraph confirms that it's still our beloved god of cunning brutality taking his time out of his day to stomp da runty gitz.