This question is not as simple as it seems. At first, you might consider that Bartolomeo Christofori is credited with inventing the piano in 1709. (Although, there are accounts of pianos prior to the 18th century.) However, the instrument that Christofori built was actually a harpsichord (the predecessor of the piano). In fact, he called his instrument, “Arcicembal che fa il piano e il forte” which translated from Italian is, “Harpsichord with soft and loud”. Eventually the name was shortened to the “pianoforte” and then simply the “piano”.
The harpsichord is a keyboard instrument that creates tone by plucking strings with duck quills. As a result, the force with which the keys are depressed doesn’t affect the volume. Christofori developed a primitive hammer action which allowed for dynamics. However, there were subsequently countless technical innovations that led to the development of the piano as we know it.
It was during Beethoven’s life that the piano experienced dramatic evolution. While Christofori’s keyboard was made entirely out of wood, little by little, metal bracing was added to strengthen the piano. By the late nineteenth century, nearly the entire inside of the piano became reinforced by a cast iron plate which supports enormous string tension. Steinway & Sons was producing a fully modern piano by the late 1800’s.
So, it is a subjective question as to when the first “Piano” was played. It depends upon how you define the piano. In the strictest sense one could argue that Christofori played the first piano at the turn of the 18th century. Or, perhaps the first piano was played by Henry Steinway! However, Franz Liszt was the first to play the piano as we know it. The first person to play solo piano recitals, Liszt transformed the instrument to a modern standard with the help of countless instrument builders. While the instrument he played was not quite a modern piano, his performances solidified the piano as we know it today.