American Tobacco Co - in 1890 and, through acquisitions and mergers, came to control virtually the entire American tobacco industry with around 150 factories. The U.S. Court of Appeals eventually deemed it in violation of the Sherman Antitrust Act and forced the company to dissolve.
Andrew Carnegie's Steel Co. - created a vertical monopoly in the steel industry by obtaining control over every level involved in steel production, from raw materials, transportation and manufacturing to distribution and finance. By 1897, he controlled almost the entire steel industry in the United States. In 1901, became part of the world's first billion-dollar business when it merged with a group of other steel businesses under the name U.S. Steel Corp. (ticker: X), to become the largest company in existence at the time, which remains among the largest steel producers in the world.
AT&T - operated as a monopoly in the telephone industry for many decades until 1982 when it was forced to break up into eight smaller companies, almost all of which have since become a part of AT&T again.