The grandpappy of high-power automatic pistol rounds, and still going strong 94 years after it was introduced to overcome the shortcomings of the .38 Long Colt revolvers used in the Philippines. The .38 wouldn't stop a drugged-up Moro tribesman, so the Spams decided that they needed more gun. This attitude has continued on, and many Americans consider that handgun calibres starting with numbers less than 4 are smallbore.
The Colt M1911 pistol (designed by Browning) was the first weapon adopted for this cartridge, having staved off the opposition from Georg Luger who had submitted a .45ACP version of his famous pistol. It was also used in the Thompson SMG and a series of Argentine Hafdasa C4 and Halcon M-1943 SMGs. It soldiered on with the M1911 until the 1990s, when it was replaced by the older 9mm Parabellum round in the rather overrated wanky Beretta M92F, which the Spam cnuts call the M9 pistol.
Many still consider the .45ACP to be the ultimate handgun cartridge, although many people find it difficult to control. High capacity (i.e. greater than 10 rds) .45ACP pistols are very broad in the grip, and the weight of the ammunition in the pistol is not insignificant. The Spams even use it in pocket pistols, such as the Glock 30 and 36. Arguably some of the more modern cartridges like .40S&W] and .357SIG (.40S&W necked to .357 to give .357 Magnum ballistics from an auto pistol).
Several "wildcat" pistol cartridges are based on the .45ACP, such as .400 Cor-Bon (necked to .40).
Not the ultimate in handgun calibre's but is the preferred calibre of the ladyboy.