The first guitar effects pedals were studio units developed in the 1940s. They were large, expensive, and too fragile for stage use. It wasn't until the 1960s, and the widespread availability of transistors, that guitars pedals would begin to take the shape we know today.
In fact, the 1962 Gibson Maestro Fuzz-Tone, the world's first distortion pedal, is still in production in a moderately smaller enclosure; and it wasn't long before other studio audio processors found their way into guitar pedals as well. Compressors, noise gates, filters, equalisers, chorus, flangers, phasers, ring modulators, tremolos, reverbs, delays, and loopers are but a few examples of the effects a guitarist can find at their feet.