www.horsesandbuffalo.com

The word cowboy referred originally to men who were employed on cattle ranches to tend to cattle. Although it is an American term it, in all likelihood, originated from the Spanish word vaquero. The vaqueros tended cattle on horseback and were the result of the hacienda system of Spain. This seems plausible because vaca is Spanish for cow, and the method of beef production that depended on allowing cattle to graze on large areas of open range was, with a few improvisations, imported form Spain to its colonies in the New World and adopted by non-Spanish immigrants groups.Check out this link here. It has been suggested that there might be an Arabic connection due to the centuries of Islamic domination in Spain. The word bakara or bakhara which was Arabic for heifer could have been the origin of vacca and vaquero.
An idealized version of the American cowboy evolved in the late 1800s helped by stories written about the American West and the image carried over into the 1900s with the introduction of movies. Cowboys were inevitable depicted as white, Anglo-Saxon and generally personifying the American ideals of self-dependency and individuality. However, in their own time period and in the areas they could be found they were often seen in a negative light. Only about half were white, and regardless of their ethnicity cowboys were on the lower rungs of society. Cowboys worked under difficult and dangerous conditions while being poorly paid. When they did receive their pay and were able to enjoy the benefits of a town, they earned a reputation for wild and careless behavior; much like sailors on shore leave.
During the 1920s “cowboy” in some circles became synonymous with reckless. This alternative meaning has continued into the present. In many circles, for example, President Bush’s foreign policy was derided as “Cowboy diplomacy”, and the President as a cowboy.