Cornelius “The Commodore” Vanderbilt – Got his start in shipping (hence the moniker) but made his fortune in the railroad industry.
John D. Rockefeller – Oil man extraordinaire. Got his start in kerosene, but eventually moved into gasoline as well.
Andrew Carnegie – Carnegie steel built American. Bitter rivals with Rockefeller… but eventually sold his business for an enormous sum to JP Morgan.
JP Morgan – Scion of “the House of Morgan”, the first real “investment banker” inherited a sizable banking empire and built it even higher. Worked with Edison, but eventually stabbed him in the back to create General Electric.
These were the “Big 4” as it were… the guys who more or less ran America. While there were many other players, these 4 are the ones you’re most likely to hear about.