I don't collect knifes, but I have always wanted one of these.
It's a vintage A.G. Russell "Sting" boot knife from the 1970's.
A.G. Russell of one of the first "Custom" knife makers of the 60's. When I was younger I read a book series called "The Survivalist" by Jerry Ahern and the main character carried one in his waist band and I've always wanted one..... now I have one.
This one was used, but I didn't want a brand new one anyway... I like to use or wear the stuff I own and getting it used was not only better, but cheaper.
They also made a fiberglass version of this knife called the "CIA Letter Opener"... no metal but quite sharp and useful.
The sheath is original to the knife as far as I know.