If you took a bighorn sheep, threw in some ox-like bulk and then added the size of an elephant, you'd have an animal that looks something like a Bantha. These beasts live on Tatooine, where they wander in herds and serve sentient masters as beasts of burden.
More specifically, Banthas typically work for Tusken Raiders, who use the hairy mammals to transport themselves and their cargo across the desert. Banthas are docile herbivores, and once their working days are up, their remains are used for food, clothing and drinks.
We can only speculate as to their evolution, but it seems a bit counterintuitive that Banthas are cloaked in heavy fur in the middle of a hot, arid climate. Perhaps their brown hair provided insulation from the heat. Maybe Tatooine was in the middle of a global-cooling spell that necessitated a warmer coat. Regardless, Banthas are a wacky combination of animal parts in a memorable form.