John D. Rockefeller's oil corporation that bought out other oil businesses.
Rockefeller merged business both horizontally and vertically to control as much of the oil industry as he could. He would choke off other oil business by cutting off cheap railroad transportation for their oil or other methods and then would buy the oil corporation as it was failing and bring it under his 'umbrella'.
A prime example of how aggresive Gilded-Age business was. It was a target of the Sherman Anti-Trust Act and remains to this day the archetype for the American monopoly.