John Browning developed a semi-automatic pistol in .32 caliber in 1896 and went on to chamber the guns in .25, .380 and .45 ACP cartridges. Note: ACP is the acronym for Automatic Colt Pistol. In 1911 the U.S. Army adopted the Browning designed and Colt manufactured .45 ACP as their official handgun, hence the name 1911.
The 1911 remained in service in that capacity for the next 75 years (1911-1985). Many say it was a mistake to replace it, to this day, this former soldier included.
A semi-automatic pistol functions by using the energy from the recoil of a single round of ammunition to extract and eject the fired cartridge from the pistol's chamber and load the next round from a magazine into the chamber for the next shot.
So just to be clear, the term automatic describes the reloading function, not the firing function. You do have to pull the trigger each time in order to fire a semi-automatic pistol.
And while the automatic-reloading has caused these guns to be referred to as automatics or autos, you still have to pull the trigger each time to fire the gun.