Unlike the
semiautomatic bolt action rifle* which is purely an invention of
gun grabbers there really is a semiautomatic revolver!
As you might suspect, this is a very good example of an answer to a question no one asked. If I recall correctly, it was a Soviet design and was peculiar in that it used the gas generated from the firing of the cartridge to recock the hammer. In effect it was a gas operated semiautomatic revolver. This gun is an extreme oddity and should be displayed alongside the other weird european guns like the rifle that had a curved barrel for shooting around corners. I am not making this up.
This revolver, aka the Webley Fosbery worked just like any other except that after every shot, the hammer would reset to the single action position, meaning it is cocked, and the operator would have to use less force in pulling the trigger to set off the next round.
Ordinarily the hammer on a revolver would stay in the lowered position until cocked by hand or, if the revolver is double action capable, when the trigger is pulled again.
Traditional revolvers are single action, like those used by cowboys in the movies, that's why they need both hands to fire quickly, one hand to aim and fire the other to cock the hammer, also called fanning a quick six. Modern revolvers now are either double action or double action only and only needs one hand, or rather one finger, to operate. Traditional double action can also be operated in single action mode by manually cocking the hammer before every shot.
*There is no such thing as a semiautomatic bolt action firearm.