Rat Fink is a character created by an artist named Ed "Big Daddy" Roth. Roth drew a big, scary-looking rat with lots of sharp teeth and a really long tail. This rat also had big eyes and usually wore a hat of some sort. Lots of people liked the Rat Fink character and started putting stickers of him on cars or wearing Rat Fink t-shirts.
The Rat Fink character was popular in the 1960s and was part of a bigger movement called "Kustom Kulture." This movement was all about cars that were customized to look different and cool. People who were into Rat Fink and Kustom Kulture would often get together and show off their cars or motorcycles.
Today, some people still like Rat Fink and the Kustom Kulture movement, and you can still find Rat Fink stickers or t-shirts if you want to show your love for this little rat with a big attitude!