>> The invention of the modern piano is credited to Bartolomeo Cristofori (1655–1731)

The invention of the modern piano is credited to Bartolomeo Cristofori (1655–1731) of Padua, Italy, who was employed by Ferdinando de' Medici, Grand Prince of Tuscany, as the Keeper of the Instruments; he was an expert harpsichord maker, and was well acquainted with the body of knowledge on stringed keyboard instruments. It is not known exactly when Cristofori first built a piano. An inventory made by his employers, the Medici family, indicates the existence of a piano by the year 1700; another document of doubtful authenticity indicates a date of 1698. The three Cristofori pianos that survive today date from the 1720s. 

Grand piano by Louis Bas of Villeneuve-lès-Avignon, France, 1781. Earliest French grand piano known to survive; includes an inverted wrestplank and action derived from the work of Bartolomeo Cristofori (ca. 1700) with ornately decorated soundboard.

Cristofori named the instrument un cimbalo di cipresso di piano e forte ("a keyboard of cypress with soft and loud"), abbreviated over time as pianoforte, fortepiano, and simply, piano. While the clavichord allowed expressive control of volume and sustain, it was too quiet for large performances. The harpsichord produced a sufficiently loud sound, but offered little expressive control over each note. A harpsichord could not produce a variety of dynamic levels from the same keyboard during a musical passage (although a harpischord with two manuals could be used to alternate between two different stops, which could include a louder stop and a quieter stop. The piano offered the best features of both instruments, combining the ability to play loudly with dynamic control that permitted a range of dynamics, including soft playing. 

Early piano replica by the modern builder Paul McNulty, after Walter & Sohn, 1805

Cristofori's great success was solving, with no prior example, the fundamental mechanical problem of designing a stringed keyboard instrument in which the notes are struck by a hammer: the hammer must strike the string, but not remain in contact with it, because this would damp the sound. Moreover, the hammer must return to its rest position without bouncing violently, and it must return to a position in which it is ready to play almost immediately after its key is depressed, so it will be possible to repeat the same note rapidly. Cristofori's piano action was a model for the many approaches to piano actions that followed. Cristofori's early instruments were made with thin strings, and were much quieter than the modern piano, but much louder and with more sustain in comparison to the clavichord—the only previous keyboard instrument capable of dynamic nuance via the weight or force with which the keyboard is played.
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