Guards! Throw these miniscule vermin into the dungeon until they are of worthier size!
~ King Goobot

Gaolers, also called Wardens or Jailers are known for keeping prisoners in check. These villains are feared for or are known to imprison their captives, whether it is in a jail cell, a cage, etc. For obvious reasons, the vast majority of these villains are Corrupt Officials. Many are also psychopaths who enjoy tormenting their victims by imprisoning them (e.g. Buffalo Bill from The Silence of the Lambs). Ironically, some Gaolers can be Prisoners themselves.

Gaolers can qualify as a Pure Evil if they imprison innocent people and torture their prisoners such as Lots-O' Huggin' Bear who acts as a penitentiary warden and broke toys physically and psychologically by making Sunnyside Daycare a hellish place as well as Infinite who tortured Sonic for six months before wanting him to be thrown out of space so Sonic can see his world become utter hell before he dies.

There are also certain kinds of Gaolers who can be known under a distinct subcategory known as Trap Masters. Trap Masters are those who are skilled at ensnaring and trapping others, thereby leaving them to be imprisoned.