Before the Elves, inheritors to the magic of the world, were even conceived of and before the continent of Ulthuan was raised from the seafloor, before the Dwarfs were even a sparkle in the eyes of the Creators, before mankind first walked the Earth, there was
Pepe, Prophet of Kek Lord Kroak, Mightiest Toad.
Lord Kroak (or Lord Kodak as autocorrect calls him) was the firstborn of the Slann, the first race created by the Old Ones (in their own image) to aid them in shaping the planet to defeat the eventual coming of Chaos. In time, the rest of the Lizardmen were created and served under Kroak. It's possible that Kroak was the one who taught the first Elves magic at the command of the Old Ones, but it could have been any or even all of the Slann.
Kroak did little in the fluff until Chaos first entered the world with the collapse of the Warp Gates, which made the world as accessible to Chaos as a planet sucked into the Eye of Terror. After holding a city-spanning forcefield up for decades during the Great Catastrophe against a literally neverending tide of Daemons, he got fed up of that and turned the field into a titanic explosion that vapourised a hundred thousand of them. As the daemons promptly pulled another infinite horde out of their asses and kept coming, Kroak proceeded to pull his sleeves up and bring out the titanic apocalypse magic that should really have been reserved for the Old Ones themselves. The army book describes it as goddamn time stopping as reality itself struggled to accommodate the tide of bullshit emitting from Kroak's mind, the world around his city folding in on itself to stem the tide of daemons.
They penetrated his defences regardless, and Kroak was ripped to shreds by no less than a dozen Bloodthirsters. Doesn't matter though, as at this point he's too goddamn powerful to give a shit about being dead, and his unstoppable spirit continues to defy them. He basically becomes the singularity at this point, as the world turns blindingly bright and the daemonic horde pretty much just stops existing altogether.
The sacrifice of Kroak is what kept the bulk of the Daemon invasion from facerolling the Elves in one day, and as a result Caledor the Dragontamer had time to set up the Vortex in the center of Ulthuan. Kroak's solo efforts freed up the rest of the surviving Slann to channel their own power into Caledor's spell, hastening the weakening of Chaos. Without his efforts the Warhammer World would have been consumed in it's infancy, before man had even left their caves and discovered agriculture.
His spirit lives on to this day, thousands of years down the line, the ghost of his old body now just echoing the titanic destruction he unleashed upon the world. The lizardmen kind of wheel him out on his hoverchair now and then if they need to nuke somebody. The mummy of his favorite Skink rests on his throne, and even in death defends his beloved master (handling all the Close Combat for him).
Kroak's Oracle from the days when he was alive, the Skink Priest Ten-zlati, is the voice of Kroak among the Lizardmen and outranks even young Slann as he knows secrets of the Old Ones not known even to Lord Mazdamundi.
tl;dr Kroak is the God-Emperor of Mankind if Emps wasn't a complete and utter fail——HERESY!.
The End Times
Come the apocalypse Kroak makes the ultimate sacrifice after the Skaven, in their foolishness, destroy the warpstone moon Morrslieb and send its remains hurtling down to crash on the planet below. After Mazdamundi dies crushing most of the fragments of Morrslieb, Kroak wills himself back to life. He isn't resurrected, he doesn't escape from the afterlife, he just decided to not be dead anymore and reality obliged. And no, he didn't use a phylactery or necromancy either (suck it, Nagash!)
Then his spirit invokes all of his power, ensuring that the devastation only affects Lustria and the Southlands; the former holdings of the Lizardmen are burnt to slag and cinders and everything dies, but the rest of the planet survives instead of being blown to bits. He also teleports some of the Lizardmen away to safety, but in the process he gets obliterated by the flames and shockwave from the impacts.
In doing this, he postponed the prophesied end of the world for a few years and, while the planet was already doomed, it may have allowed the Lizardmen temple-ships to escape safely instead of getting vaporized by the blast wave of planetary destruction. This also may have ensured the Incarnates and the core of the planet survived the Apocalypse, allowing Sigmar and the surviving Slann to colonize the Mortal Realms and eventually make the Stormcast Eternals. So yeah, Kroak probably bet for the long term.
Pretty badass for someone whose name is a frigging awful frog pun.
Age of Sigmar
And in keeping with the tradition of death being only a speed bump for Kroak... He came back in Age of Sigmar and scares Chaos and Skaven players, because that's just how Kroak rolls. Ribbit ribbit you chaos bitches.
As part of the Broken Realms, Kroak is not only returning to the scene as a fairly major player in Broken Realms Be'lakor and Broken Realms Kragnos, but he is snapping back in style. He's got a massive new model decked out with all the fineries a dead slann truly deserves and some rules (hopefully to remind Teclis who is THE wizard of the setting in case Teclis gets cocky after beating Nagash).
On The Tabletop
Given that Lord Kroak is, well, dead, you kind of don't want to let him anywhere near a fight. He's got lackluster stats for Movement (4), Strength (3), Toughness (5), Wounds (6), and Leadership (9). Oh, and anything we didn't mention is all 1's. He's an Infantry Special Character and a level 4 wizard who knows only one signature spell; The Deliverance of Itza. This is a casting value 12+/18+/24+ direct damage spell that affects all enemy units within 12/18/24 inches and inflicts 2D6 S4 hits (3D6 for Daemons and Undead of either kind). He cannot lose this spell by any means; if it is somehow swapped, stolen or forgotten, he immediately gets it back, and an enemy caster who stole it forgets it.
He's Cold-blooded, causes Fear, is Flammable, rides a Mage-priest Palanquin and is Unbreakable.
Eternity Guardians means he makes Temple Guard Unbreakable.
First Generation Spawning means he can cast his signature spell as many times per turn has he has the dice for, and he can choose to roll a D6 when he miscasts, with a 2+ meaning he takes a S6 hit and loses D6 power dice instead of having to roll on the miscast table. An Arcane Vassal he was using when it happened also takes an S6 hit.
The Spirit of Lord Kroak means he cannot drop below being a level 1 wizard.
His Supreme Shield of the Old Ones gives him a 3+ Ward save and his Golden Death Mask is a magical talisman that inflicts a -1 penalty on all To Hit rolls made against Kroak or a unit he has joined.
On the whole, he's a fun character hamstrung by his exorbitant points cost.
Age of Sigmar
He is still kind of dead, but now he is dead for immeasurable ages which means in the battleshock phase you'd roll a d6 and add how many wounds he has taken, subtract the bravery and if it's less than 1 he is fine, if it is more than one he is dead. Not only on less than one he is fine, but he heals all of his wounds which means the only way to confirm a kill on him it to do 10 WOUNDS IN 1 TURN; and for anything that could insta-kill him - looking at you Archaon and Nagash - it only does 2D6 Mortal Wounds, so you need to roll 10 or more to kill him. He also loses his Deliverance of Itza but gets celestial deliverance which is quite similar. On a 8/9/10 (he can do the spell up to 3 times) you select 3 units, on 2 ups then they suffer d3 mortal wounds (d6 if a daemon). he's not half bad in combat doing 2d6 attacks which are fairly ok, but in spells he can really go ham. 4 spells and dispells per turn, and not half bad spells at that. Also he can summon in units of seraphon (its usually skinks) and will basically never die. He is super good and nothing can stop my little toady boy.
Total War: WARHAMMER
He is finally playable!!! However, he is not a Legendary Lord but a Legendary Hero, meaning we won't be seeing him leading an army but he is sure powerful as hell. He has powerful unique spells wherein he nukes shit out of the foolish warmbloods daring to go against the Great Plan without harming his allies. This simple-but-effective spell list is: Deliverance of Itza I (powerful but weak against armor, still does a shit tons of damage) & II (much larger range and ignores armor, EVEN BIGGER DAMAGE) & III (OH LORD HE CUMMING!!). He also has the Supreme Shield of the Old Ones as an ability that gives your units in an area a sexy 44% all-round damage resistance, protect them from magic, missiles, physicals you named it! Oh, did I mention it's also has no winds cost? Passive effects he can get include a 5 more leadership bonus from his leadership aura than most others can get, resistances to pretty much everything aside from fire, -wound recovery time, 5% damage resistance for the entire army, causes terror, regeneration, +28 power reserve and -15 to the enemy because fuck them, and while he can't wound other agents (he instead can boost troop XP, replenish, growth or income), he can still get the ability to not only damage a settlement walls, but at rank 20 also its buildings and the settlement's level itself so even the hardiest capital daring to stand in Lord Kroak's way will become easy pickings - follow the Great Plan or get croaked, bitches
Lizardmen players who pick Gor-Rok as their faction get to play the game on faceroll mode because he starts with Lord Kroak and so the dynamic duo will plow a rapetrain through everything that's against the Great Plan as Gor-Rok mocks armies' pathetic attempts to kill him as Kroak fucking explodes them to atoms.
Another thing to note about him is that whenever he is doing an action, like spell casting, his spirit can be seen smacking down on the foolish enemy even in melee combat. The only bad thing that can be said about his execution in Total Warhammer is his favorite mummified skink from the tabletop is sadly nowhere to be seen.