The aurochs is the wild ancestor of the modern cow. Although the aurochs is extinct today, these animals once roamed across much of Europe and Asia, and there were the subjects of numerous works of art produced in these regions. Domestication of the aurochs appears to have occurred in India, the same region the animals originated from. For an idea of what an aurochs would have looked like, you can consult museum collections, which often have paintings or other depictions of these animals on display.
Most modern domesticated animals have living relatives, allowing people to see how they have evolved as a result of centuries of selective breeding. Modern cattle are a bit unique in this sense, as their last living ancestors died out around the 1600s, eradicated in favor of domesticated cattle. Like other wild relatives of domesticated animals, aurochs behaved significantly differently than their domesticated counterparts, and they were known for being intensely fierce and very territorial. The feat of killing an auroch was a rite of passage in some human communities, a testament to the ferocity of the auroch.
According to genetic evidence, aurochs emerged in India around two million years ago, and they spread outwards from India across Asia and parts of Europe. Different groups of aurochs evolved in different ways, as they learned to cope with different natural environments. Physically, all aurochs were larger and heavier than modern cattle, with large lyre-shaped horns and distinctive pale dorsal stripes. Unusually for mammals, the aurochs also displayed sexual dimorphism, with males and females developing different coloring.
Originally, biologists thought that several aurochs populations were domesticated independently by different human communities. However, later evidence emerged to suggest that all modern cattle are the descendants of aurochs domesticated in India. At one time, wild aurochs populations existed side-by-side with domestic cattle, until the aurochs were pushed out by human activities.
There is some dispute as to the biological classification of the aurochs. Some people believe that they were genetically distinct enough from modern cattle to be considered a separate species, in which case they are classified as Bos primigenius, while modern cattle are classified as Bos taurus. Others believe that modern cattle are actually subspecies of the aurochs, in which case they should be more properly known as Bos primigenius taurus and Bos primigenius indicus in the case of zebu.