Tru'nembra

Tru'nembra (AKA "Angel of Music") is from Ramsey Campbell's "The Plain of Sound (fiction)"

In the Mythos

And then I thought I heard a shriller, steadier note that was not from the viol; a calm, deliberate, purposeful, mocking note from far away in the West. . . . Unimagined space alive with motion and music, and having no semblance of anything on earth.
— H.P. Lovecraft, "The Music of Erich Zann"

The Outer God Tru'nembra is an entity composed of living sound, capable of manifesting as "living music". Tru'nembra may dwell or have originated in the Gulf of S'glhuo‎‎, where it seems to be served by a cult of the Denizens of that extra-dimensional gulf of sound.

Cult

Tru'nembra has no organized cult on Earth, but is followed by a cult of Denizens of S'glhuo on their extradimensional plane of sound. On Earth, Tru'nembra does sometimes capture the attention of - or is accidentally drawn to the attention of - lone Human Cultists - typically brilliant but eccentric mathematicians, physicists, inventors, occultists, and especially musicians, whose interests in increasingly outre properties of sound and sound waves might draw them toward increasingly exotic and esoteric qualities of alien music, and ultimately toward contact with Tru'nembra, whose strange music of S'glhuoan sound quickly begins to erode the sanity of its unwitting human devotees, ultimately drawing them out of the physical world and into the ultimate madness of the Court of Azathoth or extradimensional places stranger still.

Associated Mythos Elements

• location: Gulf of S’glhuo, its dwelling-place in a universe of "pure sound"
• race: Denizen of S’glhuo, who may operate organized cults in that universe
• race: Human Cultists, who sometimes make accidental contact with Tru'nembra

References

• fiction: Ramsey Campbell, "The Plain of Sound (fiction)"
• fiction: H.P. Lovecraft, "The Music of Erich Zann" (the Malleus Monstrorum draws its description from this story)
• scenario: "Malleus Monstrorum"