Whoever decided to put foot pedals on a piano? Do we know who did it, or do we only know the general period that this happened? I would like to know who did this and when did it happen?
As Indrek pointed out, this gives at least partial answers to your questions.
In short, the answer to who first put foot pedals on a piano is not known exactly, but the practice seems to originate in England. A piano of Americus Backers from 1772 might be the first one to use foot pedals instead of knee levers.
Then you have a different question in the title. The piano of Backers just mentioned had two pedals, una corda and damper, and this seems to have been the most common configuration up to the late 19th century. The French company Boisselot and Sons was the first to have a sostenuto pedal, in 1844, but it was only Steinway who some decades later made it a common device. However, more pedals (many more) were in use quite early and it's probably impossible to say who was the first one to have some three pedals (as opposed to una corda, sostenuto, damper) on their piano.