Kernel
Leonardo is the type-specimen of the Renaissance polymath. Apprenticed at Verrocchio's workshop in Florence — a vertically integrated atelier where painting, sculpture, anatomy, and engineering were taught as one subject — he leaves behind around 7,000 pages of notebooks containing flying machines, anatomical drawings ahead of their time by 300 years, hydraulic engineering proposals, and the Mona Lisa.
Contribution
Painting (a small finished corpus, but every one a candidate masterpiece). Anatomical drawing more accurate than anything else produced until the 19th century. Engineering studies of fluid flow, wave motion, gear design, and flight. The first systematic combination of geometric precision and observational naturalism.
Lineage
Verrocchio in Florence; brief stints in Milan (Ludovico Sforza), Rome, then France under François I where he died at Amboise. His notebooks scattered after his death and were not assembled in their current form until the 19th century, which is part of why his engineering ideas largely did not propagate — they were rediscovered after they had been independently re-invented.
Civilization-scale significance
The cultural archetype of the universal genius. Whether or not the actual historical Leonardo deserves that status, the archetype he installed structures every subsequent claim that one person can hold all the technologies of an age in their head.