Perhaps the most iconic aspect of the Renaissance as a whole is its tremendous artistic achievements - figures like Leonardo da Vinci and Michelangelo Buonarroti are household names in a way that Petrarch is not, despite the fact that Petrarch should be credited for creating the very concept of the Renaissance. The fame of Renaissance art is thanks to the incredible creativity of the great Renaissance artists themselves, who both imitated classical models of art and ultimately forged entirely new artistic paths of their own.
Medieval art (called "Gothic" after one of the barbarian tribes that had conquered the Roman Empire) had been unconcerned with realistic depictions of objects or people. Medieval paintings often presented things from several angles at once to the viewer and had no sense of three-dimensional perspective. Likewise, Gothic architecture tended to be bulky and overwhelming rather than refined and delicate; the great examples of Gothic architecture are undoubtedly the cathedrals built during the Middle Ages, often beautiful and inspiring but a far cry from the symmetrical, airy structures of ancient Greece and Rome.
In contrast, Renaissance artists studied and copied ancient frescoes and statues in an attempt to learn how to realistically depict people and objects. And, just as Petrarch "invented" the major themes of Renaissance thought by imitating and championing classical humanist thought, a Florentine artist, architect, and engineer named Filippo Brunelleschi "invented" Renaissance art through the imitation of the classical world.
Filippo Brunelleschi (1377 - 1446)
Brunelleschi was an astonishing artistic and engineering genius. He became a prominent client of the Medici, and with their political and financial support he undertook the construction of what would be the largest free-standing domed structure in all of Europe: the dome of the cathedral of Florence. For generations, the cathedral of Florence had stood unfinished, its main tower having been built too large and and too tall for any architect to complete. Literally no one knew how to build a freestanding stone dome on top of a tower over 350 feet high. By studying ancient Roman structures and employing his own incredible intellect, Brunelleschi built the dome in such a way that it held its internal structure together during the construction process. He invented a giant, geared winch to raise huge blocks of sandstone hundreds of feet in the air and was even known to personally ascend the construction to place bricks. The dome was completed in 1413, crowning both his fame as an architect and the Medici's role as the greatest patrons of Renaissance art and architecture at the time.
While the dome is usually considered Brunelleschi's greatest achievement, he was also the inventor of one of the most important artistic concepts in history: linear perspective. He was the first person in the Western world to determine how to draw objects in two dimensions, on a piece of paper or the equivalent, in such a way that they looked realistically three-dimensional (i.e. having depth, as in looking off into the distance and seeing objects that are farther away "look smaller" than those nearby). Unlike other Renaissance innovations that had direct parallels in other cultures, like the study of ancient texts or a recognizably humanistic approach to philosophy, linear perspective does appear to be one truly unprecedented intellectual invention originating in Europe. This innovation spread rapidly and completely revolutionized the visual arts, resulting in far more realistic drawings and paintings.
Leonardo da Vinci (1452 - 1519)
Da Vinci was famous in his own time as both one of the greatest painters of his age and as what we would now call a scientist – at the time, he was sought after for his skill at engineering, overseeing the construction of the naval defenses of Venice and swamp drainage projects in Rome at different points. He was hired by a whole swath of the rich and powerful in Italy and France; in his old age he was the official chief painter and engineer of the French king, living in a private chateau provided for him and receiving admiring visits from the king.
Leonardo's most important "scientific" work at the time had to do with human anatomy. The church banned the dissection of corpses on religious grounds - the fear was that the soul needed a site to return to during the Second Coming of Christ at the end of the world, so human bodies were not to be tampered with. Da Vinci received special dispensation from the church to perform human dissections on the bodies of executed criminals, however, ostensibly to look for the physical organ that contained the soul. In fact, he was just interested in seeing how the body worked, and his anatomical drawings inspired new generations of physicians to learn how the body functioned based on empirical observation.
Da Vinci is famous today thanks as much to his diagrams of things like flying machines as for his art. Ironically, while he was well known as a practical engineer at the time, no one had a clue that he was an inventor in the technological sense: he never built physical models of his ideas, and he never published his concepts, so they remained unknown until well after his death.
Michelangelo Buonarroti (1475 - 1564)
Michelangelo was the most famous artist of the Renaissance during his own lifetime, patronized by the city council of Florence (run by the Medici) and the pope alike. He created numerous works, most famously the statue of the David and the paintings on the ceiling of the Sistine Chapel. The latter work took him four years of work, during which he argued constantly with the Pope, Julius II, who treated him like an artisan servant rather than the true artistic genius Michelangelo knew himself to be. Michelangelo was already the most famous artist in Europe thanks to his sculptures. By the time he completed the ceiling of the Sistine Chapel, he had to be accepted as one of the greatest painters of his age as well, not just the single most famous sculptor of the time.
In the end, a biography of Michelangelo written by a friend helped cement the idea that there was an important distinction between mere artisans and true artists, the latter of whom were temperamental and mercurial but possessed of genius. Thus, the whole idea of the artist as a ingenious social outsider derives in part from Michelangelo's life.