Who is Quigley Quagmire from The Slippery Slope and what is their importance?

Quigley Quagmire is one of a set of triplets. In an earlier book, Quigley was presumed to have died in a fire, thus, Klaus and Violet are surprised to meet him in the Mortmain Mountains. Like the older Beaudelaire children, Quigley has been investigating the secret society called the VFD, and during his investigations, he discovered the secret passage through mountain caves to the valley where the VFD headquarters were located.