Leather is a material created through the curing of hides, pelts and skins of animals. Leather was a very important clothing material, and its other uses were legion. Together with wood, leather formed the basis of much ancient technology. Leather with the fur still attached is simply called fur.
In the past, most leather was treated in a process called tanning, where the hide was exposed to wood tannin which was of a low Ph, or acidic. This prevented normal decomposition and often inparted color.
Today, most leather is made of cow hides, but many exceptions exist. Some skins have during different times in history been considered very beautiful to make leather of. For these reasons certain snakes and crocodiles have been hunted to near extinction.