Caricatures are very popular nowadays (even at FN!). However first caricatures go back as far as the origin of art itself. Leonardo da Vinci drew many caricatures, and liked to seek people with deformities to use as models. There's a speculation that one of the caricatures Da Vinci drew was his humorous self-portrait (the figure at the bottom of the right half).
The point of the caricature was to offer an impression of the original which was more striking than just a portrait. In fact, the word "caricature" comes from the Italian "caricare", meaning "to load", thus the caricaturist's aim is to invest his image with as much meaning as possible.
Caricature, therefore, experienced its first successes in the closed aristocratic circles of France and Italy, where such portraits were passed about for mutual enjoyment.
Take any famous art work (painting, drawing, fresco) and turn it into caricature by exaggerating the natural characteristics of the subjects in the artwork.