Grom the Paunch
Once upon a time, there was a group of Goblins. No more interesting than any others of their race, they found themselves without a WAAAGH to join and thus decided to have an eating contest. Deciding to up the ante, one of their number dared another, a small Goblin named Grom, to ingest troll meat. Raw troll meat, which regrows faster than almost any being can digest it. Theoretically, this should have killed him since only beings like Ogres or other trolls can accomplish such a feat and not burst. After several weeks (during which the competition went on) of excruciating pain, Grom's belly bloated as the meat regrew inside him. Goblins gathered around him, waiting for the inevitable explosion of gore. It never came. Grom's body adapted, and he somehow came to digest the hunk of meat at the exact rate it regrew, granting him regenerative abilities and making him larger than any Goblin (and even most Orcs), which almost immediately made him the Boss of his small clan, the Broken Axe. Ten years later, he had become Warboss of almost all Greenskins in the southern Badlands which he added to his growing WAAAGH (because of course, you gotta have a WAAAGH). After claiming leadership of a large chunk of the Night Goblins by literally crushing their Warboss beneath his paunch, he lead an attack on the Dwarf lands and wiped out multiple Holds before having his minions chip away a statue of the Dwarf god Grungi into his own likeness. The Dwarfs regrouped and with reinforcements attacked WAAAGH Grom, fighting a three day battle to an ultimate stalemate. The Dwarfs sent messages to the Empire for aid, while the Goblins simply waited for more of their race (and their larger kin) to come from afar to see the spectacle of the fucking massive Goblin who's da biggest (resulting in most Night Goblins at the time joining him).
The Emperor at the time, Dieter IV, responded by immediately removing the capital of the Empire from Nuln, and moving it to the other side of the Empire to Altdorf where it remains to this day (End Times notwithstanding). The entry in the Book of Grudges as a result ALSO remains to this day. The High King of the Dwarfs responded by commanding the Dwarfs seal themselves within their Holds, and after a short time of rampaging through the Dwarf lands and unable to find anything to fight, the WAAAGH moved on.
Grom returned to the Badlands, and was joined by the more refined Greenskins who had learned the art of commerce using giant chariots the size of a small city to transport goods as well as the Goblins clever enough to tame Dire Wolves to ride. This marked the last time Grom walked like a common Snotling, and from that point forward only traveled by chariot.
By this point, WAAAGH Grom had come to resemble its leader; large, slow, and regenerative despite any losses suffered. When Grom finally made it to Empire lands he carved a path of destruction through the countryside, obliterating any armies or communities he came across and using everything from the largest man (slaves, navigators, and rations) to the smallest stick (can never have enough
dakka chariots, and chariots take a lot of wood). He mostly avoided cities until he reached his goal; old Nuln. While Dieter IV had moved his court, the former capital still shined with gilded surfaces and polished marble. WAAAGH Grom found little resistance as the populace fled before the sea of green outside the gates.
After taking the city however, Grom did the unthinkable. He stopped marching. Content to enjoy chariot races, swim in gold coins, and consume high class food from all over the world , he began living a lifestyle that would put many Slaaneshi hedonists and Ogre Tyrants to shame.
Disgusted by his abhorrently un-Orcy behavior, his minions beginning with the Black Orcs began to desert him and attack Empire cities in small, manageable numbers. Forest Goblins, too alien and uninterested in the affairs of their kin, saw Grom's army as a distraction they could use to surge from the Great Forest and obtain food for their spider companions and masters.
The time of Greenskin prosperity came to an end when Prince Wilhelm, cousin to the Emperor, raised a militia army and purged Greenskins from Reikland. Only the crops grown that year in the reclaimed fields saved the Empire from complete collapse. Grom, content to be the only Greenskin to have held court within an Empire city, was finally roused to battle when the voice of Gork himself (or possibly Mork) spoke to him through his Shaman Ol'Blacktoof, telling him "GO WEST YOUNG GIT!" Grom immediately commanded all Greenskins within shouting distance to mount their chariots and ride to the coast. His army completely stampeded the army of Middenland, although after Grom's chariot was destroyed by a cannonball he ordered his forces into the city of Middenheim. The populace was left completely unharmed, as the only thing the Greenskins sought was the finest wood available. The temple of Ulric lost its roof, and the city retained everything else as Grom's only desire was a replacement chariot.
After reaching the coast of Nordland, Grom demanded his boyz build ships. More ships than had ever been built by green hands were constructed, entire forests vanished almost overnight while Orcs looted entire villages, buildings and all, and were rebuilt as they had been before on the decks of the sea hulks. Many of the remaining Black Orcs, uninterested in Grom's plans, found themselves as slaves and meals to their frenzied smaller cousins.
After several months the massive fleet disembarked, and traveled south towards Marienburg. The Imperial fleet engaged them there, and after losing half their forces a freak storm kicked up which blew both fleets away from the city. The bulk of the Greenskin ships sunk immediately, having been made of da best (green) wood. For forty nights, Grom's own ship was tossed about on the ocean waves until it finally broke apart on a shore covered in mist. The survivors discovered they were in Yvresse, on Ulthuan. A land completely shrouded in magic that islands came to life and attempted to sink ships, in a region where that same magic manifested Daemons into existence when the (non-magic) wind blew. Grom was the first, and last, WAAAGH to reach the birthplace of the Elvish race.
Very few of Grom's animals had survived the cruise; a handful of the most feral Wolf alphas who had consumed their packs to survive and one Wyvern, which would only obey Ol'Blacktoof. Although the Greenskin numbers were low, Yvresse was the least populated High Elf kingdom and thus even the warband of the Goblins and few Orcs remaining outnumbered the army of the city of Tor Yvresse, the only major settlement. Ol'Blacktoof, who had become a very powerful wizard by this point, sensed the Waystones of the land drained magic from the world and informed Grom they should be destroyed. Each one that fell destabilized the magic of the world more, warping reality and causing an aurora borealis effect of deadly beams in eight colors at all times. Drawing the energy into himself, Blacktoof lost himself more and more as the voices of Gork and Mork (or Mork and Gork) grew more and more distant and other voices grew louder.
Tor Yvresse, once the greatest city in the world, had become a ghost town occupied by barely enough Elves to fill one of its many opera houses or market squares as constant threat from the worst horrors of the world and the cold climate had driven less hearty Elves to more paradisiacal kingdoms. Despite this, the defenders of Yvresse were among the most skilled warriors alive, having every day been tested against the worst horrors the Warp itself could offer. Grom's army met the army of Tor Yvresse within sight of the city walls. Grom's strategy was simple; use his entire army in an offensively useless anvil, while his chariots attacked from behind. Both of Grom's forces were devastated, but he alone killed enough Elves to keep their force from being wiped out. In three days of unending battle, all Elves outside the city were dead including the Prince who ruled the entire region and the Goblins began to loot their gear to construct warmachines for a siege. As they worked, the beams in the sky began to cross; the loss of the Waystones had begun to destabilize the world. After one day of bombardment, the city infrastructure was ruined; defenders were isolated as bridges fell, defensive points for arrows to rain from collapsed, and magical wards lost power. Goblins pushed into the city unhindered. Rather than the hints of civilized conduct they had shown in Nuln, Grom's small force rampaged through the streets in a manner that would put Beastmen to shame, torturing the innocent and destroying everything that looked like it had been made with intent. The Chaos Gods, sensing the weakness of the Vortex, shook the world in mighty earthquakes that caused widespread destruction and threw the aim of the famous Spire Guard off, ensuring unhindered advance for the Greenskins. Ol'Blacktoof and his Wyvern abandoned the forces below, making for the tallest tower in the city which dwarfed mountains.
At that moment, a new force entered the city; a massive army of Elves, far better equipped than army Grom had ever seen, arrived seemingly from nowhere. The leader of the force, a regal Elf with nothing but hatred in his heart after seeing the devastation of his home, beheaded Ol'Blacktoof as he passed him on his gryphon Stormwing on his way to the tower. There, Eltharion and his two trusted Mages attempted to calm the Winds of Magic and save the world. Nobody knows what happened exactly other than the two Mages were never seen seen again and from that day forward, the cocky and roguish Eltharion carried the demeanor of a driven and mistrusting general with a one hundred yard stare. Grom's army was caught between battle-hardened veterans in front, and rallied defenders from the rear. Most of his army immediately fled, including Grom himself. Driven to the sea and the remains of their wrecked ship, all Greenskins were slain and the land burned to prevent the spores from rooting. Eltharion went on a rampage across the Old World, destroying Greenskins to the point Goblins everywhere would fear Elves.
Elves claim Grom's ultimate fate was waddling into the ocean and drowning. Goblins who knew him claim Grom would never walk, and that he either caught Ol'Blacktoof's Wyvern and made for new lands to continue WAAAGH Grom, or else rode a magic Elf chariot straight up one of the Annuli mountains. As many years have passed with no hint of Grom, most assume he is dead. It was revealed by a BL author that Grom is dead. Eltharion, on a solo mission, Hunted him down, Tortured him in ways that would put the dark elves to shame, then fed his body piece by piece into a magical furnace. The Grim kept this to himself since he didn't want the other elves to know he sunk to such levels of barbarity.
Grom had an archenemy in the form of Git Guzzler in earlier editions, although it was unclear if Grom ever actually knew Git existed or what happened to Git after Grom died. After his death, and possibly that of Git Guzzler as well, rulership of the Night Goblins passed to Skarsnik.
On The Tabletop
Grom's been around for a couple of editions, generally being a Goblin Warboss in a suped-up chariot with Regeneration, a magical axe, and granting immunity to the Fear Elves rule of his fellows. As of 8e, this is what he looks like:
If somehow forced to be taken out of his chariot (which is S5, T4, 3W, Armor Save 5+ Scythed Wheels, pulled by 3 Giant Wolves), Grom is a Movement 4 (despite his obesity) WS5 BS3 S4 T4 W3 I4 A4 LD8 infantry character. He wields the Axe of Grom (+2 Strength, Killing Blow, Elfbane [Killing Blow is 5+ against Elves]), can Regenerate, he is immune to the Fear Elves rule, as are all other goblins in the army, and he can call Grom's Waaagh! and give +1 to combat resolution for the rest of the player turn to all goblin, wolf rider, night goblin and spider rider units.
Grom's chariot also comes with Niblit, who gives him an extra WS3 S3 I2 attack and causes Grom to count as the Battle Standard Bearer, carrying the Lucky Banner (5+ Ward Save for Grom and Chariot), though Niblit is killed if Grom's chariot gets destroyed, and both Niblit and the chariot will die if forced to retreat from close combat (though Grom runs away as normal).
Players wanting to use him could use the Avatars of War "Goblin King Krork Toadgobbler" model and put it on a Boar Chariot.