Single-shot pistols are theoretically the simplest pistols. The earliest handguns were single-shot, muzzle-loading guns with ignition provided by inserting a smoldering match cord into a touch hole. As such, they were essentially nothing more than miniature cannons, small enough to be handheld.
Improvements followed in subsequent centuries, as various types of locks (ignition devices) were invented. In the matchlock, the separate match cord was affixed to a spring-loaded pivot which could be tripped by a trigger. In the wheellock, a mechanism analogous to that used in today's cigarette lighters replaced the smoldering match cord. In the 17th century, the flintlock, which strikes a flint against steel, appeared. (The flintlock, amazingly, remained state-of-the-art for some two hundred years.) In the 19th century, percussion caps were developed, followed shortly by modern integrated-primer cartridges, and hammers therefore traded their flint for firing pins.
Single-shot pistols continue to be manufactured today and are often used for handgun hunting game, including big game. The most powerful handguns are capable of taking all game including elephant.