Guardian of the guardian(s) of the gold

Where does that expression come from? As in "Who is the guardian of the guardian(s) of the gold" or "Where is the guardian etc..."
The griffin [gryphon" is the mythological creature who guards the gold , but , usually its own gold.] My "guardian" is the one who keeps the guardians of other peoples' gold honest. But I still don't know where the expression originated or was coined. Help, please.

I suspect this is a direct relative of the Lat*n expression (which I can't precisely remember!!) but which translates as 'Who is the custodian of the custodians?'. It is centuries old and, I believe, dates back to ancient Rome.