Helya

Helya is the ruler of Helheim, an underworld realm for Vrykul who fail to ascend to Odyn's Halls of Valor.

History
Originally, Helya was the titan-forged watcher and daughter of Odyn, one of the appointed Keepers of Azeroth. She was involved in crafting the Elemental Plane, alongside Highkeeper Ra, as a prison for the Elemental Lords. She was responsible for the creation of the Halls of Valor, as Odyn disapproved of the Pantheon's judgment in empowering the Dragon Aspects. As a result, Odyn ordered her to tear off a section of Ulduar and raise it into the sky.

Odyn declared that the Halls of Valor would be home to all Vrykul who died a worthy death in battle to become his Valarjar, believing they would better defend the world than dragons could. To accomplish this, however, Odyn required vrykul to become undead in order to freely traverse the Shadowlands. No one would voluntarily make this sacrifice, and so Odyn decided to forcibly create these subjects. Helya was outspoken in her disagreement and threatened to return the Halls of Valor to Ulduar.

In response, Odyn destroyed her physical form and transformed Helya into the first Val'kyr. It immediately became her duty to ferry souls from the Shadowlands and create more unwilling Val'kyr. Meanwhile, Odyn concealed the reality of Helya's transformation by claiming she had reached out to the power of the Shadowlands herself and wound up consumed by the realm of Death, transforming her. According to Odyn's story, she had suffered for her arrogance and emerged begging for Odyn's forgiveness and the right to become his first Val'kyr.

Helya's resentment for Odyn grew over the span of millennia until Loken offered her the opportunity of freedom from Odyn's service if she would turn against him. Using the same magic involved in the creation of the Elemental Plane, Helya trapped Odyn and his Valarjar within the Halls of Valor and created her own realm, known as Helheim, where she would care for Vrykul souls in her own way. Such souls would become Kvaldir under her sway.

During the Third Burning Legion Invasion of Azeroth, Warchief Sylvanas Windrunner drew the Horde's forces to Stormheim. Following an Alliance attack on the Horde, Sylvanas made her way to Helheim alone in order to strike a deal with Helya in exchange for the Soulcage, a magical item that could be used to subjugate Eyir. Later, at an unknown point in time, Helya came to acquire the soul of Illidan Stormrage. It is speculated that this was done to fulfill a deal with Gul'dan.

After the revelation that Odyn's stormforged Valarjar could be converted to Kvaldir, he decided to finally take action and employed adventurers from beyond the Broken Isles to dispatch Helya. They were successful in slaying her, freeing Odyn from his prison as well as saving Illidan's soul. Despite this, Helya did not seem to stay dead, as her Kvaldir have continued their activities and that Helya herself was growing in power once again. The Valarjar did not seem surprised by this, stating that one cannot kill death.