There are many types of “cows”, if you are talking about bovines. The females of the genus Bos are used for milk, and both species are used for meat. Bos includes your average dairy cow and the huge (extinct) Auroch. Other bovine-like animals include the bison, Cape Buffalo, and yak. Not all bovines are as calm and docile as your average dairy cows. In Spain and Mexico, bullfighters fight pretty aggressive bulls (male cows), and the Cape Buffalo of South Africa is considered an extremely aggressive animal when provoked.
The gentle dairy cow is a product of domestication. You probably know about evolution being due to the selection of the “best adapted” traits, which may be physical or behavioral. The bovine from which cows probably evolved were similar to the extinct Auroch – a pretty intimidating wild cow. Domestication by humans selected the most docile animals to breed generation after generation, giving rise to a much more docile animal. A similar process resulted in dogs being evolved from wolves.