Disparaging term first coined in 1934 by historian Matthew Josephson to describe industrialists of the late 19th century. Such industrial leaders as Andrew Carnegie and John D. Rockefeller had gained a reputation for flaunting their wealth in the face of company towns and the urban blight in which their workers lived. During the Great Depression, such men were being viewed as evil in the eyes of the public, so the term gained widespread popularity.
The so-called "robber barons" were obsessed with efficiency, centralization of their production methods and "vertical integration" of their processes by controlling raw resources, manufacturing and sale of the final product. For example, Standard Oil under Rockefeller owned its wells, refineries and controlled the railroads used to transport consumable oil to market.
Those who defended the "robber barons" saw them as industrial leaders who improved and modernized productivity and strengthened the nation's ability to compete internationally. The public, in general, had great disdain for them... an attitude that was not helped by such infamous statements as William Vanderbilt's "The public be damned!"