Leonardo da Vinci is known as many things; painter, inventor, sculptor, architect, scientist, musician, mathematician, engineer, author, anatomist, geologist, astronomer, botanist, paleontologist, cartographer, and time-traveling superhero. Wait.... WHAT?! No, you did not read that incorrectly, Leonardo da Vinci is actually a time-traveling superhero, well, at least in the Marvel Comics universe.
When one thinks of Leonardo on paper, they typically think of the Vitruvian Man or the Mona Lisa, not Marvel Comics, but it's true that he is on that page as well. First appearing in Astonishing #54, Leonardo debuted in the comic world in October 1956. Since then, Leonardo's integration into the larger Marvel-verse has grown, and so too has the weird and wild things he has done.
Leonardo put his great mind to use for the betterment of society as a member of the group the Brotherhood of the Shield. The Brotherhood of the Shield is essentially an ancient version of what S.H.E.I.L.D. is today, a long-lasting secret organization whose top priority is keeping all life on earth safe. The group comprised of famous minds throughout history, with other members including the likes of Imhotep, Sir Isaac Newton, Zhang Heng, and Galileo. While the Avengers sure get a lot of credit for saving the world, it was actually this supergroup of history's greats that were the first heroes to take down Galactus and the Brood as well as turn Celestials back.
Being the student of learning that he is, Leonardo took it upon himself to study the Phoenix Force after a messenger from K'un-Lun reached out to him. It was here in his studies that Leonardo helped the Iron Fist of the time earn her title, giving her the determination she needed to take on Shou-Lao the Undying, all while he used his telescope to keep an eye on and study the coming Phoenix.
Not long after, Leonardo mastered time travel. He decided to put his inventing skills to use, creating a robotic copy himself that he could leave behind to live out his normal life as he bounced around history. He then traveled throughout time, seeming to have a deep interest in the 1960s, placing him amongst the time of some of Marvel's most well-known heroes and escapades. It was here in the modern-day that, under the alias Aries, Leonardo formed the Great Wheel of Zodiac, a secret organization consisting of the world's most elite intelligence agents, even including Nick Fury and his brother. Unfortunately, this group eventually split up, forming the many different secret organizations of the Marvel universe such as S.H.I.E.L.D., Leviathan, the Zodiac Cartel, and even Hydra. That's right, in a way Leonardo caused the creation of both S.H.I.E.L.D. and Hydra.
While he has no actual powers, one could liken Leonardo da Vinci to the mind of Tony Stark, just a Renaissance age version; he even builds himself a flying mechanical suit of armor. His super genius, engineering ability, and quick wit allow him to rank up there with some of Marvel's best heroes despite him technically having no super abilities of his own.