Leon M. Leon is credited as the true inventor of the Clapboard. Originally a prop and gag man in silent films, he was a pioneer sound man when "talkies" began.

As he often explained, the clapboard was merely an accident. It's evolution began as a separate slate, along with two wood blocks that he clapped together for the sound synchronization. Holding the slate and two blocks were cumbersome, so he asked a crew member to hinge the two blocks together. However, when the camera couldn't clearly see the two blocks as they hit, he ran some tape diagonally around the closed blocks, and then slit them apart with a knife.