Gaspards?

So are there any gaspards out there who might search for Has ultrà metas requiescunt beatam spem expectantes and find themselves here? If so, I’m trying to find the origin of the term “gaspard” as used to describe the people who live in the subterranean tunnels of Paris. None of my French dictionaries define this term.

I thought it loosely translates to “sewer rat” but my Petit Robert doesn’t list it which is very odd as I thought it listed ‘mature’ argot. I think the word shows up any time history books report people hiding underground (political rebels, criminals etc) in the French capital?