Murmur was a demon who was leader of the Cult of the Elder Elemental Eye. He was able to turn nightmares into flesh and blood and was also capable of possessing people when they slept. He possessed one of the officers of the Firestorm Cabal and use her to recruit members of the cabal into the Cult of the Elder Elemental Eye. Murmur was destroyed in 1479 DR in a fight with the deva Demascus and his friends. Demascus believed Murmur was from a reality outside Toril's universe. This proved to be correct, as Murmur was in fact a fragment of the Voidharrow, a dead universe that served as the prison of Tharizdun.
In his true form Murmur had black limbs and strange liquid crystal blood.