The Hattifatteners are silent beings that are forever wandering around in large herds. The only thing that interests them is reaching the horizon – and once they reach it, their journey continues. The white, faceless Hattifatteners are deaf and dumb. They do not need to eat or sleep but become electric in a thunderstorm.

The Moomins first encounter the Hattifatteners in the story The Moomins and the Great Flood.