Leonardo da Vinci was a painter, sculptor, architect, cartographer, engineer, scientist and inventor in the 15th century. Yet, despite his genius, he referred to himself as "senza lettere" (the illiterate, the man without letters). For good reason: until late in life, he was unable to read, or write, Latin, the language used by virtually all other Renaissance intellectuals, the lingua franca, akin to English today. Nor was he acquainted with mathematics until he was 30. Leonardo was born out of wedlock but was raised by his real father, a wealthy Florentine notary. He served at least ten years (1466-1476) as Garzone (apprentice) to Andrea del Verrocchio and painted details in Verrocchio's canvasses. Only in 1478, when he was 26, did he become independent. He was not off to an auspicious start. He never executed his first commission (an altarpiece in the chapel of the Palazzo Vecchio della Signoria, Florence's town hall). His first large paintings were left unfinished ("The Adoration of the Magi" and "Saint Jerome", both 1481). Most of the sketches and studies for Leonardo's works of art and engineering are found on his shopping lists, personal notes, and personal expenditure ledgers. No one was allowed to enter Leonardo's den, where he kept, as Giorgio Vasari in "Lives of the Artists", describes: "a number of green and other kinds of lizards, crickets, serpents, butterflies, locusts, hats, and various strange creatures of this nature". Leonardo's clients were often dissatisfied with his glacial pace, lack of professional discipline, and inability to conclude his assignments. He was frequently involved in litigation. The Cofraternity of the Immaculate Conception sued him when he failed to produce the Virgin on the Rocks, an altarpiece they commissioned from him in 1483. The court proceedings lasted 10 years. The head of Jesus in "The Last Supper" was left blank because Leonardo did not dare to paint a human model, nor did he trust his imagination sufficiently. Leonardo worked four years on the Mona Lisa but never completed it, either. He carried it with him wherever he went. Leonardo's terra cota model for a colossal bronze sculpture of the father of his benefactor and employer, Ludovico Sforza, was used for target practice by invading French soldiers in 1499. The metal which was supposed to go into this work of art was molded into cannon balls. Leonardo was a member of the commission which deliberated where to place Michelangelo's magnificent statue of David. His cartographic work was so ahead of its time, that the express highway from Florence to the sea - built in the 20th century - follows precisely the route of a canal he envisioned. His scientific investigations - in anatomy, hydraulics, mechanics, ornithology, botany - are considered valuable to this very day. Bill Gates owns some his notebooks containing scientific data and observations (known as the Codex Hammer). But Leonardo's loyalties were fickle. He switched sides to the conquering French and in 1506 returned to Milan to work for its French governor, Charles D'Amboise. Later, he became court painter for King Louis XII of France who, at the time, resided in Milan. In 1516, he relocated to France, to serve King Francis I and there he died. Leonardo summed up the lessons of his art in a series of missives to his students, probably in Milan. These were later (1542) collected by his close associate, Francesco Melzi, as "A Treatise on Painting" and published in print (1651, 1817).