I want to make Clear that I am no Expert on Pocket knives.
I do know a bit about them but I do know where to look for Info.
The Best Source for that kind of information is always one of Bernie Levine's Books.
I am paraphrasing here:
The Trapper is a Jack Knife.
It is Specifically one that has two blades.
These Blades are both Pivoted from the same end of the frame.
One Blade is a Clip Point and the Second is a Long Spey Blade.
The pattern is thought to be post 1900.
The thinner version of the Trapper was introduced in the 1920s and the mini-Version was actually not introduced until around 1970.
are usually about 4.5 inches Closed but are Twice as Wide as a Standard Trapper.
(Heavy) are in 4 to 4.5 inch length Closed.
are usually in the 3.775 inch to 4 inch range closed and thinner in Style.
The Mini Trapper
(Baby) is usually 3.250 to 3.5 inch in length Closed and built in the same size as the Light or even thinner.
The Most Common Case or Frame is the Swell Center Regular Jack Pattern and the Premium Versions are sometimes built in the Common Serpentine Pattern Frame.
I would say that the Trapper is an American Pattern. it is not one of the Sheffield Designs.
I am sure Trappers were and still are made all over the world but the pattern was made for this market.
Anyone who has interest in knives should try to find a Copy of Bernie's Book.
Levine's Guide to Knives
1st, 2nd,3rd or 4th Edition
Last I checked A.G. Russell Still had some and they were about $75.00.
It is a bargain for the knowledge contained.