The Sound Keeper is a woman who keeps all the sounds made in the world filed away in alphabetical order in her fortress, which is like a mansion. She is an elderly woman in a black dress and pointed hat reminiscent of what a witch might wear.
The Sound Keeper is quite kind and hospitable and very neat. She likes music and also silence, which she 'listens' to. However, she also talks a lot, which Milo finds ironic. What's even more ironic is that even though she cursed her kingdom to complete silence, she doesn't obey the silence herself. Like the other rulers in Wisdom, the Sound Keeper has lost sight of what her people really need. Without Rhyme and Reason there to keep an overall balance, she tries to control what her subjects should value. In her case, this means taking away all the sounds and protecting them from ungrateful listeners. She dislikes sounds which she considers unpleasant so she locks them up, along with unneeded sounds, which take on physical form in her fortress. However, a few years ago, up until the events of the book, she decided to lock up all sounds, regardless of whether she found them unpleasant or not, and nobody knows why, although there had been speculation that it was either the weather, something to do with the moon, or the absence of Rhyme and Reason, the latter theory is being supported by the fact that the Sound Keeper had started behaving oddly around the time the princesses were banished. Although The Sound Keeper is actually being a tyrant, she thinks she's doing the right thing. When her fortress is destroyed and the sounds are released, Milo apologizes, but the Sound Keeper wholeheartedly says it's her own fault because "you can't improve the sound by having only silence. The problem is to use each at the proper time". The Sound Keeper learns that she needs to do things in moderation, and she can't have everything under her own control.