Leonardo da Vinci is credited with depicting an early ball-bearing design.
Around 1498, Leonardo studied ways to reduce friction between moving parts. His sketches show balls placed between rings or surfaces so that rolling contact would replace much of the sliding friction. This principle is the basis of the modern ball bearing.
Leonardo did not invent every later form of bearing, and his drawings were not mass-produced industrial components. Instead, they are important evidence that he understood how rolling elements could improve mechanical movement. His studies appeared in notebooks concerned with machines, motion, and friction.
A common mix-up is calling Leonardo the sole inventor of the modern ball bearing. Earlier rolling supports existed, while standardized steel bearings developed much later with industrial manufacturing.