Before becoming "SEPTA", under prior owners it used to be called "Philadelphia Transportation Company" (PTC), and before that, it was called "Philadelphia Rapid Transit" (PRT).
There was also the Philadelphia Suburban Transportation Company, aka the Red Arrow Lines. The former Philadelphia & Western Railroad became SEPTA’s Norristown High-Speed Line. The “Regional Rail” lines are formerly the property and operations of the Pennsylvania and Reading railroads, save the Center City tunnel that was built by the city of Philadelphia.