Smith & Wesson did not invent the double-action trigger mechanism, but they have sure used the idea a lot. The invention is a distinction that falls to one Ethan Allen, who obtained a patent for the idea in 1837. In partnership with Charles Thurber, Allen designed and produced a single-shot, screw-barrel pistol that was revolutionary.
The hammer, made from tubing, had no spur because it could not be cocked. Pressure on the trigger caused the hammer to rise to its fullest extent, then release to fire. In today’s world, it would likely be called a “double-action-only.” The basic concept was executed by various makers in many ways and that continues today. It’s just a nifty way to have your gun arranged, particularly a fighting gun. Eventually, the idea was applied to many revolvers, including Pettingils, Remingtons, Coopers, even Colts. And in 1929, Walther of Germany introduced the first truly successful double-action self-loading pistol.