Final answer:
Jay Gould is the "robber baron" who made his fortune in railroads through exploitative business practices.
Step-by-step explanation:
The "robber baron" who was notable for the exploitative way he made his fortune in railroads was Jay Gould.
Gould bought older, smaller, rundown railroads and made minimal improvements. He then capitalized on the demand for transportation by charging high prices. His business model focused on financial profit rather than tangible industrial contributions. Gould controlled over ten thousand miles of track across the United States, accounting for 15 percent of all railroad transportation.