Eberron: Rising from the Last War describes Sul Khatesh as “the Keeper of Secrets and the Queen of Shadows. She embodies the fears and superstitions surrounding magic, from malevolent warlocks to mad wizards, from deadly curses to magical power that draws those who wield it deeper into darkness.” She may be bound beneath Arcanix, but she has found ways to spread her influence further. Her prakhutu—the First Scribe, Hektula—has written books of magic that can grant tremendous power but that also serve as a focus for her influence; these could mirror the effects of the Book of Vile Darkness or the Demonomicon.
Sul Khatesh spreads cults and covens, and where her
cultists come together to perform malefic rituals, Sul
Khatesh can touch the world. While she often whispers
to her warlocks and to other susceptible minds, Sul
Khatesh is essentially dreaming; her whispers rarely
work out well for those who listen to them, but they
aren’t all tied toward one grand plan. The agents of
Sul Khatesh are a strong force in the Lords of Dust.
Hektula maintains the Library of Ashtakala and often
mediates disputes between the other speakers.
Source: Chronicles of Eberron
Aundair is a land of wisdom and magic, but terrible things are hidden beneath its soil. An overlord is buried deep below the earth near the floating towers of Arcanix, hidden under tons of rock and held in bondage by the Silver Flame. Her name is Sul Khatesh, but she is more commonly known as the Keeper of Secrets, for she knows more about dark and arcane matters than any mortal could comprehend. For now, she slumbers—but she can prove a threat even while she is sleeping. Occasionally, she touches mortal minds in her dreams, and some of the greatest mystical innovations of the Arcane Congress might have been inspired by her whispering words. Few of those inspired by this ancient muse understand what they are dealing with, and her gifts might bring madness or unforeseen disaster. Her exarch is Hektula, called the Shadow Scribe, the librarian of Ashtakala, the Demon City.
Source: Eberron Campaign Guide
Sul Khatesh is known as the Keeper of Secrets and the Queen of Shadows. She embodies the fears and superstitions surrounding magic, from malevolent warlocks to mad wizards, from deadly curses to magical power that draws those who wield it deeper into darkness.
Sul Khatesh is subtler than the Rage of War. She empowers warlocks and whispers secrets into the minds of wizards and artificers, helping them master spells and create relics they could never shape on their own. But few of those inspired by Sul Khatesh understand what forces they are dealing with, or recognize the danger inherent in her gifts.
The Queen of Shadows. An entity of shadow, Sul Khatesh can assume any form. Her favored shape is a twelve-foot-tall humanoid figure draped in a flowing, hooded robe formed of swirling mist and clinging shadow.
Minions. Most of Sul Khatesh’s followers are wizards and warlocks, and she is one of the primary patrons for warlocks in Khorvaire. Covens devoted to the Queen of Shadows use dark magic and fear to dominate whole communities, while isolated warlocks make pacts with Sul Khatesh to pursue power and revenge. By sharing her power in this way, the overlord perpetuates the image of the evil warlock, inciting fear that strengthens the Keeper of Secrets even more.
Sul Khatesh’s chief agent among the Lords of Dust is the rakshasa Hektula, who serves as the librarian in the demonic citadel of Ashtakala. Known as the First Scribe, Hektula presides over an immense trove of arcane knowledge and artifacts.
Source: Rising from the Last War
I know the secrets that shape the world. With three words, I can kill with fire; with four, ice. But why should I, when I can bend you to my will? The Queen of Shadows reveals your secrets—do as I command, or all will learn what you’ve hidden.
The overlord Sul Khatesh embodies the fear of both magic and of secrets . . . for what is magic but secret knowledge? She whispers insights to students at Arcanix and inspires evokers working on weapons of war. But she also encourages people to keep secrets, and then sets misery in motion when she reveals these secrets to those who would use them.
Sul Khatesh’s cults often begin as transactional. Wizards or would-be warlocks invoke her with rituals, offering blood or service in exchange for power and knowledge. Sul Khatesh has no need of mortal souls, but a cultist might believe they have sworn their soul to her. What truly delights her is when magic is used for cruel purposes or in ways that cause people to fear it. While cultists may forge a bond for rational reasons, the more people that draw on her gifts, the more that corruption can creep in. Members of the Court of Shadows believe that they are part of a shadow kingdom that becomes more real with each day; some members even believe they can see its towers and spires overlapping the structures of the real world. Other cults may become obsessed with their own power, embracing the idea that those who can do magic are superior to those who cannot—that it is their right to prey on these mundane cattle. Given her love of secrets, the cults of Sul Khatesh are almost always hidden and subtle. While magic usually plays a role in her cults, she could certainly have one that deals purely with blackmail and the manipulation of secrets.
Forces. Sul Khatesh’s supernatural agents are primarily rakshasa, often with greater mystical power than their comrades. Her prakhutu Hektula is the librarian of Ashtakala and perhaps the most knowledgeable sage in existence. Beyond this, her primary agents are mortals she has lured into her service and gifted with arcane power.
Gifts. Those who serve the Keeper of Secrets are usually well supplied with scrolls and magic books, and cults could be given wands or rods crafted in Ashtakala. As Sul Khatesh’s primary gift is knowledge, she might instead lead her followers to a cache of Dhakaani treasure or other hidden troves. Sul Khatesh is well known for bargaining with warlocks, and she can grant lesser spellcasting abilities should she choose.
Character Ideas. Sul Khatesh can be an excellent patron for a warlock. Her gifts are versatile; depending on the powers you seek from her, she could grant the features associated with the Archfey, Fiend, or Hexblade patrons. The primary question for such a warlock is whether you still serve her—whether you are seeking to rise in the Court of Shadows even as you go about your adventuring career—or whether you regret the bargain that you made and are trying to find a way out. Any spellcaster could have received a boon from Sul Khatesh even if they don’t have the close bond of a warlock; did she teach you your first spell in your dreams, and are you afraid she’ll return to call in this favor? Likewise, a character who wants to take the Magic Initiate feat could frame this as a sudden gift from Sul Khatesh—but what’s the catch?
Story Ideas. A cult of Sul Khatesh is an easy way to introduce an evil wizard or cabal of warlocks using their gifts to terrify and dominate a community. The Court of Shadows could fill this role, but it could also be used in a more subtle way; perhaps nobles of the Court assist the adventurers, and they are drawn into the politics and intrigues of this imaginary kingdom. A cult of Sul Khatesh could be at the center of a web of blackmail that’s tearing a city apart. A player character or NPC could suddenly find that they know the worst secrets of everyone they meet . . . but are they sure all of these secrets are true? Or is Sul Khatesh feeding them just enough truth that they’ll start believing these insights without question, even if it leads them down evil paths?
Source: Exploring Eberron