Final answer:
The 'robber baron' who made a fortune by exploiting the railroads was Jay Gould.
Step-by-step explanation:
In the context of the question, the 'robber baron' who made a fortune by exploiting the railroads refers to Jay Gould. He was a prominent railroad magnate during the 19th century and was known for his exploitative business practices.
Gould bought older, rundown railroads and offered minimal improvements. He capitalized on the desire of factory owners to ship their goods on railroads, which were becoming increasingly popular and cost-efficient.
Gould's business model worked well in the American West, where the railroads were still scattered and forced farmers and businesses to pay high prices to use his trains.