A Cleaner is a rank in Division meaning that the person holding that rank is responsible for "cleaning" up after Division ops; whether this is killing witnesses, disposing of evidence, killing romantic entanglements or cleaning up bodies. Cleaners may progress on to becoming a Guardian.
Cleaners are notably above the law, and have been known to sway the authorities with their power. Cleaners also use superior technology to dispose of bodies, to the point where it is rather easy for them to make a murder seem like an accidental death.