Beams are the support structures for the Dark Tower as well as a form of connection between various worlds, keeping reality stable. When the Beams fall (due to the Crimson King’s interventions), the worlds begin to collapse.

A billy-bumbler is a raccoon-dog-like creature native to Mid-World. Intelligent and capable of limited speech, billy-bumblers are loyal and perceptive. Oy, a beloved member of Roland’s ka-tet, is a billy-bumbler.

The Dark Tower is the axis of all existence, standing at the center of space and time. It holds together an infinite number of universes (including many of Stephen King’s other novels). The Tower is supported by six Beams, each guarded by animal totems. When the beams fall, reality collapses. Roland’s quest is to reach the Tower and prevent the collapse of all worlds.