Reapers

"'Because I could not stop for Death...' - Emily Dickinson, 'Because I Could Not Stop for Death'"

Summary
Reapers, alongside AETHER, The Face of the Master, the Quilters, and the Tickers, are responsible for the upkeep of reality and ensuring its continued function. They are responsible for both ensuring that things die or fade away when they are scheduled to, and that new things are born when they are scheduled to in their place. Reapers are Celestial Horrors.

They are not part of the "Servants of Reality," but at least one has been tasked with ensuring that they are kept imprisoned until they are needed.