Okay, everyone has heard of Leonardo da Vinci and agrees that he was a genius on many levels. His technical skill as an artist is self-evident. Because of his universal popularity, I won't go into too much detail about his life, only touching on parts that I identify with.
Leonardo da Vinci was born in Italy and spent much of his life working for royalty as an inventor, scientist, and artist. Though da Vinci is best known for his paintings, I was always much more struck by his drawings and studies. I see myself as a scientist and observer of nature more than an artist; art is merely my means of reporting my findings. I identify with da Vinci's broad range of interests, especially in nature, anatomy and aging faces (see images below). I find that the best way to understand the world around me is through intense observation. As an artist and scientist, Leonardo came to his revolutionary belief in empirical observation as the foundation of all knowledge, leaving an unshakable intellectual legacy for centuries to come.
Leonardo produced studies on loads of subjects, including nature, flying machines, geometry, mechanics, municipal construction, canals and architecture (designing everything from churches to fortresses). His studies contain designs for advanced weapons, including a tank and other war vehicles, various combat devices, and submarines. Leonardo's interests were so broad, and he was so often compelled by new subjects, that he usually failed to finish what he started. I fall into this dilemma myself on occasion, having to force myself to remain focused.