Originally a clever bastard, later the head of the Strigoi Bloodline of Vampire Counts. He's about as unlucky as they come, and were it not for the forces of the universe conspiring to make his life hell he could have succeeded where other pathetic failures hadn't and conquered humanity.
Like the other Bloodline pat/matriarchs Ushoran was originally a nobleman from the province of Lahmia in Nehekhara, the Warhammer Fantasy analogue to ancient Egypt. Cousin to Queen Neferata, he was the first noble to become suspicious when she stopped aging and sucked on the maids a bit longer than she used to. She caved and told him about her experimentation with Nagash's cursed cookbook, and gave him a sip of the elixir causing him to become the second Vampire in existence. While his fellows included his bitchy cousin, a roid monkey obsessed with polishing his sword, a NEEEEEEEEEEEEEEEEEEERD that he was a bro to, and possibly cousin Neffy's husband (that one is dubious), he was a bit less...insane than the others. Ushoran was an asskissing diplomat who could get along with just about anyone and could bluff his way into you thinking he was your kinsman without effort.
He cultivated his own Bloodline within the court, biting and turning nobles he favored more than others and building a small group of followers. After the living of Nehekhara destroyed the Lahmian kingdom he fled with the others to the resurrected Nagash's Black Pyramid and joined his army under coercion and bribery. After the army's defeat at the hands of the living Nehekharans, the forces of Sigmar, and the Skaven he attempted to unite the Vampires under his command and rebel against Nagash. The other Bloodlines refused to follow him however, and after a day of battle against one another went their separate ways.
Mourkain: Rise and Fall
Meanwhile a Necromancer called Kadon, who was the son of the chieftain as well as being the shaman of the Lodringen tribe (which had been neglected by Sigmar's unification), had found Nagash's Crown of Sorcery in the hands of the corpse of Alcadizaar washed up on the shore of a river. The crown instantly filled his mind with knowledge, and he used his newfound necromantic powers to reanimate the corpses of the dead to serve the living. A massive tomb was built for the body of Alcadizaar which also doubled as Kadon's palace and a place of burial for the Lodringen. Mourkain (known as "Morgheim" to the Empire) became the name of the capital city, while Strygos became the name of the people. Ushoran and his followers at this point crossed the impassible mountains separating the land of the Tomb Kings from the Old World and immediately used his charm to become the main adviser to Kadon. The two of them made a powerful and expanding empire that rivaled that of THE Empire of the time, and Kadon worked with Ushoran's more arcane-minded Vampire servants to create many powerful magical items as well as refine the magic of Nagash into the current Lore of Vampires used by the Vampire Count army.
In the meantime, Ushoran rebuilt his Bloodline from the loyal citizens of Stygos then channeled the most dangerous power in the two Warhammer settings (common sense!) and instituted laws prohibiting his minions from feeding on the populace: they drained the blood only of the willing, or of criminals, prisoners, and slaves. The protection of the Vampires combined with the growing power and luxury provided by the wise rulership of Kadon made the people of Strygos very loyal to their rulers in a way that rivals that of current Bretonnian Peasantry. Once the kingdom had grown enough in power, Ushoran sent messengers to the other Bloodline leaders with plans for a united Vampire race. Only W'soran answered his invitations. The two of them further refined the Lore of Vampires and created many more magical objects, eventually unlocking the full power of the Crown of Sorcery for Ushoran's use.
So at this point, things were going fantastically for Ushoran and the Strygos. As one might expect, this is the point in the story where everything went to hell.
Neferata had taken the invitation of Ushoran as an implication that she was to serve him. She was so incensed by the idea that another Vampire would rule over her like she had all of them only a short time (by Vampire reckoning) ago that she manipulated the young Empire into gathering an army and attacking Strygos. While he could have easily beaten them and added the Empire to his ranks, an Orc WAAAGH had gathered both due to Abhorash and the first Blood Dragons nearly wiping them out in the nearby mountains and the slow encroachment of the Strygos on their lands. The greenskins destroyed a straight path to the foot of Mourkain itself. While Ushoran and Kadon devastated both armies, Kadon was slain and the Strygos and Strigoi forces took massive casualties to the point that the greenskins and Warboss that remained were able to smash through the city gates and destroy it. Ushoran and his remaining Bloodline held the line near the rear of the city so that the human population, fanatically loyal to him, could flee to the distant hills. At this point W'soran and his followers betrayed the Strigoi (according to the Necrarch account because the Crown of Sorcery had begun to take control of Ushoran and W'soran wanted to save the only man he had ever considered a friend, although this would hardly have been a bad end for them as he had worshiped Nagash as a god shortly before draws the story into doubt). W'soran weakened the Strigoi until they could no longer stand against the WAAAGH, and after being beaten by Ushoran fled for his life to the mountains. The kingdom of Strigos fell and became know as the Badlands to the people of the Old World.
Ushoran was separated from his kin during their retreat and seemingly crushed under a sea of green, so the remaining Strigoi Vampires broke ranks and fled in different directions. Without leadership, the Bloodline degenerated and most gave into their animalistic urges. Where before they had been restrained to non-lethal blood drinking or to consuming the dregs of society, they indulged themselves to the point that a single Strigoi was capable of consuming all living creatures from mice to giants for miles before rest. The other Bloodlines became exceedingly hostile to the Strigoi. The appearance of a Strigoi in the midst of an area controlled by Lahmians brought Witch Hunters on their heads, so Lahmians were quick to personally kill them or hire mercenaries to put them out of their (their meaning the Lahmian's) misery. The von Carsteins saw them as beggars, and did to them as the inspiration for their Bloodline did (hint: it involves fire and impalement). The traitorous Necrarchs saw them as a source of crafting materials with which to make new monsters and dissected them with glee (although they DO still trade with them and make deals with them, as Necrarchs are smart not to burn their bridges entirely). The Blood Dragons saw them as mere beasts to slay and drink the blood of for a challenge. As a result, Strigoi Vampires became more and more a group of loners.
During the early centuries of the Empire, the threat of Vampires was considered very real. The first Witch Hunters relentlessly pursued the Strigoi Vampires, despite the ineffective forces knowing very little about them. More often they attacked the people of Strigos, who has since become Warhammers gypsy analogue and lived on the outskirts of most towns and cities in the Empire. As the years went on, the mistreatment of the Strigos grew until many (often those in positions of political clout amongst the isolated clans) began to behave as the Witch Hunters believed them to have always been: witches, necromancers, and seekers of Vampirism. Ironically, the attacks of the von Carsteins under Vlad made the Witch Hunters far less focused on Strigos, but FAR more effective at hunting the Vampires themselves. But the damage had been done, and the Strigos are oftentimes the allies of Vampires who in turn usually treat them with a degree of respect (to the point that a Strigoi Vampire may literally ONLY restrain his urges from preying upon the gypsy Strigos bands...and instead consuming every man, woman, child, and animal in the nearby Empire town then fleeing resulting in the Strigos moving in to loot and live, benefiting the still loyal Strigos greatly).
For his part, Ushoran did NOT die. He has lived primarily in isolation, learning that his kin from other Bloodlines were far less loyal than ordinary mortal humans and that his own Bloodline, however loyal when he was around, were weak willed without him.
During the time of the Three Emperors of the Empire, the Strigos were persecuted more than they ever were to the point that genocide of their race made one of the Elector Counts more eligible in the eyes of the Empire. Needless to say, Ushoran was NOT impressed. He wiped out an entire greenskin WAAAGH that threatened the Strigany who had returned to the city of Mourkain, then single-handedly wiped out the forces and leaders who had sought the destruction of his gypsy followers. The leader of the group, the Elector Count of Averland, was turned and made one of the Strigoi Bloodline: Ushoran enjoyed watching the former tormentor struggle with his Vampirism, with the man only capable of restraining himself out of fear of becoming like the other Strigoi. Ushoran returned to Mourkain and sent a call for his Strigoi Vampire family and his Strigany human one to return to the city to rebuild.
Age of Sigmar
"They say I'm crazy, HA! I'LL SHOW THEM, I'LL SHOW THEM ALL! Won't I, Mister Sqeaky-Bones?! FILTHY FUCKING BARBARIANS, REEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE!"
- – Ushoran, upon escaping the Shroudcage.
In Age of Sigmar, Ushoran somehow managed to survive the complete destruction of the old setting. Nagash initially trapped him in a cage called the Shroudcage, this was in part by everyone's favorite golden idiot deciding to smash it, because it's one of nagash's toys. Ushoran escaped, although now he has gone completely mad and sees himself as a noble of high refinement in a court of majestic gold, with his followers as regal men and women behaving as if they are what they see. This madness is contagious, and his new Ghoul Kings (called Abhorrent Ghoul Kings) cause this delusion to any of their followers by proximity. Ushoran has been running amok through the setting and the Realms, infecting any locals to join his insane and rabid "noble courts" and consume those who are disagreeable to their delusions. These factions join all sides, draw from all sides, and war against all sides in an unpredictable clusterfuck that messes with everyone equally. Nobody likes them, and Nagash is actively hunting them down with a promise of great rewards for any being who comes to a Mortarch with any information on Ushoran (said reward is probably some form of undead, maybe rank in Nagash's forces).
Thanks to him appearing everywhere and his contagious insanity affecting those he comes in contact with, he has picked up an impressive list of new names and titles his followers across creation have given him.
As a side note apparently when he survived the end times gave him a make over and made him handsome, Until he started insulting Neferata which she cursed him to look ugly which is what caused him to flip his shit.
Unlike other Vampire Bloodlines, the Strigoi mostly lack central leadership. During the seclusion of Ushoran they spread out throughout the Old World, giving in to their base natures and degenerating into hulking brutes. Initially they ate solid food out of inability to restrain themselves and often vomited it up as Warhammer Vampires are mostly incapable of consuming anything but blood without conditioning. Strigoi Vampires eventually overcame their weakness, becoming almost as capable of digesting anything as an Ogre.
Strigoi rarely find themselves in the company of others for long, although Ghouls being the human equivalent to themselves are the company they are found in more than anything else. Rare is the Strigoi capable of much advanced thought, but those that are (for various reasons like being only given to periodic indulgence rather than constant, regaining some level of self control after a traumatic event, almost starving to death and returning to rational thought, conditioning by another intelligent being, or the rare guidance of Ushoran) will seek out Strigos Necromancers, resurrect Zombies (who despite being slower than molasses running uphill to the frustration of feral Strigoi, are simple enough to animate and useful as minions), then advance the goals of Ushoran or join the von Carsteins. The most intelligent (or the most feral and powerful) can easily find themselves beasts to tame or packs to join amongst the various monsters of the world. The Necrarchs can be quite helpful at assisting them in both cases.
On the Tabletop
Ushoran has never had a model. Only released in 6e where Vampire Counts saw a trimming of their named characters rather than additions, he remains something that can only be emulated on the tabletop.
If you want to use him, it's tempting to use a Strigoi Ghoul King. Remember though, Ushoran never gave into his primal nature. Although he somehow came to resemble his Bloodline (unless this is an illusion of his to inspire kinship amongst them anyway), he still retains his intelligence. Being a manipulative bastard, he should be used as a Vampire Lord kitted out like a Lahmian with abilities like Beguile. He should also have Necromancers, representing his loyal Strigany followers.