St. Leah, born Leah, was the ward of Deckard Cain and the biological daughter of Adria and Aidan/Diablo. Though originally sired and fulfilling her purpose as a vessel for Diablo, Leah's spirit would survive, and she would later be resurrected. She ascended into sainthood and defeated the Prime Evil Diablo herself.
This character is an expansion on the already canon character. For more information visit here.
From the outset, Leah was conceived as a host for Diablo. While the three Prime Evils had masterminded their exile to Sanctuary, Diablo had taken the plan one step farther. He would become the Prime Evil, combining the essences of the Great Evils into a single form. And to do that, he would need a vessel to inhabit.
To this end, when Prince Aidan struck down Diablo in the Tristram Cathedral and bound himself to the soulstone in the hope of containing Diablo's essence, the demon had been given the means to fulfill his plan. Not long after Aidan's 'victory,' he met the witch Adria, who realized that Diablo was influencing the prince. By Diablo's will, Leah was conceived and born a year later in 1264.
While Aidan became corrupted by Diablo and so became the Dark Wanderer, Tristram fell to the forces of Hell. Adria escaped with Gillian and the two made their way to Caldeum. Adria set up wards around Gillian's residence and departed, leaving the barmaid to care for the infant.
Leah had a hard time growing up in Caldeum. She would be under the care of the mentally unstable Gilliam, and would also suffer terrible nightmares. Eventually she would come under the care of Deckard Cain.
Over the next thirteen years, Leah and Cain (or "Uncle Deckard" as she called him) would hunt for artifacts and lore across the world that would help them piece together the Prophecy of the End of Days. Other areas of study included that of the Vizjerei and their (supposed) summoning of demons. Cain also tried to teach her how to control her abilities, which he told her came from her mother. His Horadric knowledge formed the basis of his teachings, but it never really helped. Still, he never gave up on her.
Eventually, after twelve years of travel and with Leah now a young woman, the two-headed for New Tristram. With Cain still in pursuit of the prophecy, he spent his days poring over the tomes and manuscripts found in the ruined Tristram Cathedral. Leah split her time between looking after him and helping out in the town.
The End of Days
Leah would prove instrumental when schemes of Diablo would come together. She worked tirelessly with her uncle to piece together the unknown, and when he died carried on his work. During this period she aided the Nephalem and the fallen Archangel Tyrael, working against the machinations of the Prime Evils. Leah would also meet her true mother Adria, learning to control her magical skills and bonding with her mother.
When Azmodan's legions were defeated and the Lord of Sin imprisoned in a powerful sinstone, what should have been a celebrated victory turned into despair. Adria showed her true colors and turned the stone on Leah, revealing that Diablo had conceived her as a vessel for future use. The powers of the seven Evils were transferred into her, her mind shattered as a result. The heroes grieved, but circumstance dictated the action. Diablo had possessed Leah but had no intention of stopping there. Rather, he departed for the High Heavens, intent on finishing the Great Conflict once and for all.
The Prime Evil
Outside the Diamond Gates, Diablo, still in Leah's body, was confronted by Imperius. The archangel turned Solarion on him, prompting the demon to reveal his true form, which came from the seven Evils merged into Diablo's being. It was partially feminine; when Diablo had possessed Aidan and Albrecht, he had been a hulking brute, their greatest fears made manifest. Leah was no different in this regard. When the Prime Evil emerged from the torrent of Solarion's holy flames, he was slim, with iconic horns and spikes, what appear to be remnants of breasts, and pronounced hips, as well as multiple mouths. Hellfire burned within his form at all times, engulfing the Black Soulstone plunged deep into his chest.
Ultimately, Diablo was cast down. Unlike Aidan and Albrecht however, whose mortal forms had remained Leah's body was nowhere to be found. Diablo's physical form crumbled into dust as he fell from the Silver Spire, leaving only the smoldering Black Soulstone to be discovered later.
The Soulstone would be destroyed by the rouge Archangel Malthael, and the many demonic spirits trapped within it were released. Leah's own tortured soul was freed as well, but remained afloat and lost in the world. Her spirit would continue to drift along, until it was gathered up by Diablo, trapping her within his growing body. She remained so for a long time, and few knew that she even was alive. Leah did not give up hope though, continuing to fight even from beyond death even trapped within the body of the Lord of Terror.
Return and Ascension
Leah would be given a new mortal form thanks to the sacrifice of the Servant. During the Battle of Westmarch Diablo engaged in combat with the human and angel armies. The Servant and the Guardians of Sanctuary fought the Lord of Terror themselves, and the Servant, finally finding Leah at last, use up all his power to free her from Diablo's grasp. Her soul was reborn as an angelic figure, clad in golden robes, ethereal rings, and empowered by the holiest of magic. Leah, with the Guardians, personally slew and contained her father's soul, trapping it and ridding the world of his evil forever.
Leah, now empowered beyond that of any mortal and perhaps even greater than the Archangels, helped establish a permeant deal with the angels and became the self-proclaimed guardian of Sanctuary. With the Prime Evils contained and the Guardians of Sanctuary at the ready, no demons dared invade Sanctuary, and the angels agreed to remain relatively distant. Leah herself created the Cathedral of Hope above the ruins Tristram, and settled into her new position of protector of Sanctuary. In particular, she acts the currant ruler of the kingdom of Khandurus, due to her technically royal blood (daughter of Prince Aiden) and the various reforms and protections she offers.
Leah is now adored (though worship of her is strictly forbidden despite a small but widespread saintly cult) as one of humanities greatest heroes, given the title of Saint. The religion of Zakarum, reformed by the Servant, sees her as the greatest champion of mankind, and at least one paladin orders exist in her name. She is best known for her compassion, diligence, and kindness, a symbol of hope, and a patron of knowledge, and most importantly, a figure of redemption.
Personality and Traits
Leah is a kind soul and arguably a sensitive one as well. Leah tended to see the good in people and be hopeful, and remains so today, despite all she has been through. In her new saintly form, she is said to be quite stunning, with long black hair, a fair face, and deep shining eyes. In her natural form she appears with pale blue skin, though she often assumes a more human appearance. Thanks to her ascension she glows like angels and possessed angelic wings, which she can easily hide. She is usually depicted in white hoods or bright clothing.
Leah, while originally not a fighter, is proficient in a bow and this has become her signature weapon. She had inherited powers from Adria (and, most likely, Diablo). These included prophecy/foresight and a degree of magical ability. Her powers surpassed Adria's own, as well as Garreth Rau's. Through most of her life, her powers only manifested when she was in grave danger. It wasn't until she was reunited with her mother that she was able to wield these abilities at will to a certain extent. Said abilities were strong enough to give Maghda pause, destroy the gates of Caldeum, resurrect Zoltun Kulle's spirit, and contain the Evils within the Black Soulstone.
After her ascension, Leah's abilities were magnified, although in various degrees. She has been known as the White-Weaver, able to cast great magical spells and perform miracles. Though not limitless, her powers are great and serves as a warning to any intruder who would dare threaten Sanctuary. This great power has even given Imperius pause. Leah is also a seeker of knowledge, and continues to add to her store of lore from the Great Library of Tristram.