The Brown Bear is one of the most aggressive creatures in the game. It is larger then the average Black Bear and may be the same size as the Polar Bear.
The Brown Bear can often be found in the open, no matter where it is. However, they don't spawn in deserts or snow biomes. They can also be found in caves, just like hyenas.
The Brown Bear seems to have its own personality, which is aggressive. They will kill you in at least three bites, if not four or five. Like all other animals they have the ability to eat, usually preferring meat over other things like plants.