Quiet Librarian

The Quiet Librarian was a malevolent ghost that acted as the central villain of the children's horror-show Are You Afraid of the Dark? episode, "The Tale of The Quiet Librarian."

History
Prior to becoming a ghost the Quiet Librarian was known as Mercy MacGregor and lived from 1895 until 1910. During her life, she was an exceptionally strict and cruel woman who valued silence to an unnatural degree and would regularly kick out disruptive children or punish them via locking them in a basement room labelled the "Quiet Reading Room".

After death, Mercy would transform into an insane and evil spirit that haunted the library, armed with a demonic box that allowed her to capture sounds from her surroundings as well as the souls of her victims - who would then be trapped for all eternity in the Quiet Reading Room, unable to make any noise and thus suffering in silence forever.

She would eventually be defeated when the children protagonists of the story (Laurie and Jace) worked together to overload the demonic box with a sound-effects toys. This caused the Quiet Librarian's own evil magic to turn against her as the box was destroyed, freeing all the souls she had captured. It also completely destroyed the spirit, reducing her to nothing but dust.