Kustodians of Exedor

This topic might have a better name.

Species names are usually singular

Talk about it here.

The Kustodians of Exedor were ethereal beings composed of pure light who guarded Exedor. (PROSE: Who Isn't Who?)

According to the Eleventh Doctor, they changed the spelling of "custodian" so as to appear more interesting. (PROSE: Who Isn't Who?)