Leonardo Da Vinci has been a hero of mine since high school, so this is a very exciting one for me to answer. While most people know Da Vinci for his paintings, he actually did not do that many. As an artist, he had many ways of expressing himself and was also considered a sculptor, architect, and draftsman (a draftsman is similar to an architect but does detailed technical drawings of machines and infrastructure). In fact, when Da Vinci was lobbying his de'Medici patron for a job, he sold himself not as an artist but as a military engineer. He completed several projects in this vein—including drafting the plans for the diversion of the Arno River to deny Florence's enemy, Pisa, access to the sea.
Da Vinci was also a scientist. Like most Renaissance artists, he saw art and science as intertwined, and so to become a better artist, he studied the science of anatomy. Da Vinci dissected both animals and human cadavers, and some of his drawings were some of the earliest, accurate depictions we have of the human body. He also independently studied botany, zoology, geology, hydraulics, aeronautics, and physics. History, theology, and politics did not interest him—most of the science he studied seemed to be more about how things moved and interacted with each other rather than what they were.