"The definition of the true savage does not concern itself even with how much more he hurts strangers or captives than do the other tribes of men. The definition of the true savage is that he laughs when he hurts you; and howls when you hurt him."
- – G. K. Chesterton
"Sickly, sinful, spectacles stand, shuffle, shamble and saunter shamelessly in mine scandalized sight! I suggest a solution... Surely such sedition should sour and succumb to Sigvald - the salacious, scandalous and sensational servant of Slaanesh! Son of Succubi, scion of sordid acts and slayer of squalid serfs!
See how I stroll, stride, swagger and swirl, spin, and slash and stab at stupid, senseless scum! Soon they shall swoon, shall seek solace and death from sundry and torments wrought on them by my strategic, severing, scintillating shower of shimmering strikes!
Send for the sword - summon Sliverslash!"
- – Sigvald the Magnificent, alliterating like a boss during the Sliverslash quest battle
Imagine Joffrey Baratheon growing up, and gaining the favor of the god(dess) of being a colossal narcissistic asshole FOR being a colossal narcissistic asshole, along with getting demigod powers and an army of sick fucks. That's who's the Sigvald is. He's also a pithy wordsmith. (Magnifissscchent!)
Sigvald was born from an incestuous relationship between a powerful warlord and his sister. Sigvald was beautiful from birth, save for a horned birthmark on the back of his neck. He grew into a strong, skilled warrior who was spoiled by his father until expelled from his tribe by his father due to Sigvald's cannibalism... ahem, "fondness for human flesh". Sigvald proceeded to murder his father in his sleep and departed for the Chaos Wastes, earning Slaanesh as his patron the next day. Soon Sigvald marched at the head of an army devoted to himself, eradicating anything he deems to be ugly, crude or irritating.
Sigvald has burned down cities on a whim; he destroyed the Bretonnian town of Chamburg because he once got a bottle of wine from there that he didn't like. Other exploits include declaring war on a province of the Empire because he broke a nail on a warrior priest's armor during a previous battle, and heading to Ulthuan to scalp as many High Elves as he could because they were more renowned for nice hair than Sigvald was.
He is spoiled by Slaanesh and is extremely self-centered: in addition to the above, his body-guards bear mirrored shields so that he may preen himself or admire his reflection in the midst of battle. His gifts from Slaanesh have left him beautiful on the outside, but rotten inside. The ground literally reshapes itself for him and his feet float an inch above the world's surface. He wears an armor of ensorcelled gold that never rusts or gets dirty and fights with Sliverslash: a rapier of silver forged from the sword of Slaanesh.
He appears a few times in the end times, first ravaging Kislev. After this he makes his way to Bretonnia where he heads the siege of Parravon. His forces overwhelm the Grail Knights and forcing Gilles to retreat, but not before he kills Sigvald's right hand man. Chaos Joffrey then goes on to take a break from fighting and turns Parravon into his own personal paradise, feasting on the finest flesh Bretonnia has to offer. Much to his dismay, the Chaos Gods pick him up and put him in Middenheim, where he is one of the few chaos champions worth a name still living. He throws a hissy fit about not having his mirror eunuchs, and offers Mannfred a spot as a replacement. He was one of the warriors tasked with killing Valten before he reached Archaon, alongside Valnir and Wulfrik, but lounges on the stairs preening himself while the other 2 duel. He makes an excuse that he doesn't want to fight Valten because he deserves to fight the real Sigmar, and prances off to parts unknown.
He is still alive during the final battle, leading forces of daemonettes against Nagash's army. Archaon had ordered him to fight alongside the troll king Throgg, a prospect that horrified Sigvald due to Throgg's hideous appearance (with Throgg teasing Sigvald over his foppishness and squeamishness). So he tried to kill Throgg and split their forces up after the deed.
Sigvald fought Krell in a badass battle, and was doing badly at first since Krell is stronger (despite Sigvald being S5 while Krell is S4, though Krell's axe gives him +2S, never mind) and more durable. Then Krell cut his pretty face and broke his sword. Sigvald saw his reflection with the one eye Krell didn't ruin and went absolutely berserk, beating Krell down with his bare fists and mangling his perfect hands in the process. After stabbing Krell through the eye socket with the remains of his sword and killing him, Sigvald's rage was spent. In that moment of clarity Sigvald saw in his mirrored shield that his face was ripped to shreds and his hands were mangled to the point where he couldn't use a weapon (though Sigvald's armor meant that his injuries would heal, all Sigvald cared about was that at the present moment he wasn't pretty).
While Sigvald sat next to Krell crying over his temporarily ruined beauty, Throgg the Evertrollsen approached. He had survived Sigvald's attempt on his life and wasn't happy. Throgg bashed Sigvald's skull in then lifted his loincloth and urinated on Sigvald's corpse. Thus Sigvald's final moment in the End Times was a well-dressed professional who got blindsided and pissed on by a smelly troll.
Age of Sigmar
He's back and even hornier than before! Evidently Slaanesh has missed our favorite Fabio look-alike and decided to elevate him into a full-fledged Daemon Prince.
After the End Times, Slaanesh refused to claim Sigvald’s soul because he/she was ashamed of Sigvald for the degrading end he'd suffered at Throgg's hands. Nagash, seeking vengeance for Krell's death, found Sigvald's soul but refused to destroy it because he loves long-lasting punishments. Sigvald's soul was shoved into a shadeglass mirror by Nagash, who also cursed it to reflect an idealized version of the viewer so Sigvald would (literally) never be seen again, then chucked it into Shadespire. Later, the city itself later ended up in Uhl-Gysh for unrelated reasons (see Warhammer Underworlds).
Unfortunately, Nagash didn't know Uhl-Gysh was also where Slaanesh was imprisoned. Being so close to his patron allowed Sigvald to regain some awareness and power over his broken soul, and grew stronger suckling on motes of Slaanesh's power. The mirror was discovered by an expedition of Kharadron dwarves, who were overcome by reflections of themselves becoming filthy rich, as per the mirror's curse. They took the mirror to a desert in Shyish, and obsessed over it to the point of letting themselves waste away like Narcissus from Greek mythology.
By this point Sigvald had regained enough power to influence his prison, and soon the mirror was found by the Scarlet Cavalcade, an army of Godseekers led by the Chaos Lord Reshevious. Sigvald used his control of the mirror to show Reshevious the most twisted and grotesque reflection Sigvald could imagine. Outraged, the proud Reshevious shattered the mirror and the whole situation caught Slaanesh's attention. Impressed by Sigvald's cleverness and resourcefulness, Slaanesh gained new interest in Sigvald and gave him another chance, not only restoring Sigvald but empowering him further. Sigvald stepped out of where the mirror once was and the entire Scarlet Cavalcade, including Reshevious himself, fell to their knees in adoration and pledged themselves to the reborn Sigvald.
Sigvald's first act was to slaughter one-sixth Scarlet Cavalcade to test his new powers, but the fanboy/fangirl-ism was so strong the survivors followed him anyway. The next order of business was a killing spree against Troggoths in revenge for the death (and golden shower) that Throgg gave him in the World-That-Was. This culminated in a battle against a massive troll army, with Sigvald personally dealing a humiliating fate to their leader. Since every Slaanesh-worshipping Chaos Lord and their mum now had pieces of Slaanesh's sword as weapons, Sigvald wanted better, so he went to Slaanesh's palace and got the deity's favorite daemon-smith to forge him a new sword made from the shards of the mirror that once imprisoned him, naming it Shardslash. Taking up the title Geld-Prince, probably for his golden armor and not because he had his balls cut off, but with Slaanesh you never know... he is now gathering his hordes in preparation for the Dark Prince’s return.
Despite this, Sigvald has a secret shame. He has a scar hidden on his body from his death in the World-That-Was. Since Krell and Throgg are dead - and you can bet Sigvald doesn't care that he'd already killed Krell - Sigvald shifted the blame to Krell's master, Nagash. But Nagash is beyond his power, and even Sigvald won't risk the Shyish Nadir. As a result, Sigvald found a new target for his revenge boner (pun intended), the empire of the Ossiarch Bonereapers. Sigvald wants to destroy the Ossiarch Empire, and is leading an army towards it. Making every servant of Nagash he can get his hands on suffer undignified fates, Sigvald wants to harm Nagaash's realm as much as possible.