The Borchardt C93 was probably the first commercially successful semi-automatic pistol.  It was designed in Germany by Hugo Borchardt in 1893, and fired a 7.65mm cartridge, also designed by Borchardt.  The gun uses a toggle-lock system to lock the breech.  When the gun is fired the recoiling assembly is driven back and one of the toggle arms is forced to rotate when it hits the rear of the frame.  This breaks the ‘knee’ joint  alignment and the breech can then fly open, eject the spent cartridge, and pick up a fresh round on its return stroke.  The Borchardt was rather cumbersome to fire, and Borchardt’s assistant, Georg Luger, took the mechanism and improved it to produce the more familiar Luger parabellum pistol.