It was a harpsichord maker named Bartolomeo Cristofori who invented the piano in 1700. Cristofori (pronounced kris-TOFF-or-ee) (1655-1731) was from Padua, in the Republic of Venice in northern Italy. He primarily built harpsichords and experimented with new designs, as became customary for builders of keyboard instruments up to the end of the nineteenth century.
Cristofori's invention was referred to as an "Arpicembalo," literally a "harp-harpsichord," that "produces soft and loud" (ch fa' il piano, e il forte). This later became a clavicembalo col piano e forte ("harpsichord with soft and loud"), and this name was eventually condensed into simply pianoforte and later just "piano."
The term "piano" is actually absurd. "Pianoforte" sounds as ridiculous to an Italian speaker as "softloud" does to English speakers!
A keyboard instrument that produced a voluminous sound like a harpsichord yet that was also capable of dynamics, or variations in loudness, was long considered desirable. Cristofori's accomplishment lay in the instrument's action, which enabled hammers to strike the strings and immediately return. The piano's principle of sound production is similar to striking a bell: A bell must be struck quickly and immediately left to vibrate, lest the vibrations be dampened. So it is with piano strings, in which the period of contact with the hammer is as short as possible to allow them to vibrate and hence produce sound.
The oldest surviving piano was built by Cristofori in 1720 and is on display at the Metropolitan Museum in New York. It was painstakingly restored to playable condition by Stewart Pollens, who managed the Met's collection of over 5000 instruments for three decades, until 2006.