Rat Fink is one of the several hot-rod characters created by one of the originators of Kustom Kulture, Ed 'Big Daddy' Roth. Roth's hatred for Mickey Mouse led him to draw the original Rat Fink. After he placed Rat Fink on an airbrushed monster shirt, the character soon came to symbolize the entire hot-rod/Kustom Kulture scene of the 1950s and 1960s. Although Detroit native Stanley Mouse (Miller) is credited with creating the so-called 'Monster Hot Rod' art form, Roth is accepted as the individual who popularized it.
The Rat Fink is a green, depraved-looking mouse with bulging, bloodshot eyes, an oversized mouth with yellowed, narrow teeth, and a red T-shirt with yellow 'R.F.' on it.
A Rat Fink revival in the late 1980s and the 1990s centered around the West Coast grunge/punk rock movements. The term fink was originally underworld slang for an informer, comparable to 'stool pigeon', and ratfink is an intensified version of 'fink.' By the time Roth used this name for a character, the term had started to pass into more general usage. It is also thought to have been a toned-down form of 'ratfucking,' a slang term for playing dirty tricks.
What's it worth? Take a look at this Rat Fink price guide: sold listings for a value indication.