The Smith & Wesson Model 36 is a revolver chambered for .38 Special. It is one of several models of "J-frame" Smith & Wesson revolvers. It was introduced in 1950, and is still in production.
The Model 36 was designed in the era just after World War II, when Smith & Wesson stopped producing war materials and resumed normal production. For the Model 36, they sought to design a weapon that could fire the more powerful .38 Special round in a small, concealable package. Since the older I-frame was not able to handle this load, a new frame was designed, which became the Smith & Wesson J-frame.