From Wikipedia

David is a masterpiece of Renaissance sculpture sculpted by Michelangelo from 1501 to 1504. The 5.17 meter (17 ft)marble statue portrays the Biblical King David in the nude. Unlike previous depictions of David which portray the hero after his victory over Goliath, Michelangelo chose to represent David before the fight contemplating the battle yet to come.  It came to symbolize the defense of civil liberties embodied in the Florentine Republic, an independent city state threatened on all sides by more powerful rival states and by the hegemony of the Medici themselves. This interpretation was also encouraged by the original setting of the sculpture outside the Palazzo della Signoria, the seat of civic government in Florence. The completed sculpture was unveiled on 8 September, 1504.

The history of the statue of David precedes Michelangelo's work on it from 1501-1504. Prior to Michelangelo's involvement, the Overseers of the people of Office of Works of the Duomo (Operai), comprised mostly of members of the influential woolen cloth guild, the Arte della Lana, had plans to commission a series of twelve large Old Testament sculptures for the buttresses of the cathedral of Santa Maria del Fiore. Until then only two had been created independently by Donatello and his assistant, Agostino di Duccio. Eager to continue their project, in 1464 they again contracted Agostino to create a sculpture of David. He only got as far as beginning to shape the legs, feet and the figure, roughing out some drapery and probably gouging a hole between the legs. His association with the project ceased, for reasons unknown, with the death of his master Donatello in 1466, and Antonio Rossellino was commissioned to take up where Agostino had left off.

Rossellino's contract was terminated, soon thereafter, and the block of marble originally from a quarry in Carrara, a town in the Apuan Alps in northern Tuscany, remained neglected for twenty-five years, all the while exposed to the elements in the yard of the cathedral workshop. The rain and wind weathered it down to a smaller size than was originally planned. This was of great concern to the Operai authorities, as such a large piece of marble was both costly, and represented a large amount of labor and difficulty in its transportation to Florence. In 1500, an inventory of the cathedral workshops described the piece as "a certain figure of marble called David, badly blocked out and supine." A year later, documents showed that the Operai were determined to find an artist who could take this large piece of marble and turn it into a finished work of art. They ordered the block of stone, which they called The Giant, "raised on its feet" so that a master experienced in this kind of work might examine it and express an opinion. Though Leonardo da Vinci and others were consulted, it was young Michelangelo, only twenty-six years old, who convinced the Operai that he deserved the commission. On August 16, 1501, Michelangelo was given the official contract to undertake this challenging new task. He began carving the statue early in the morning on Monday, September 13, a month after he was awarded the contract. He would work on the massive biblical hero for 2 years.