Leonardo da Vinci sketched an ornithopter, a flying machine intended to imitate the flapping motion of bird wings.
His Codex Atlanticus and other notebooks contain studies of bird anatomy, wing structure, and mechanisms for transferring human power to wings. Leonardo understood that human muscles alone would probably not provide enough power for sustained flight, but his designs explored the engineering problem in detail.
An ornithopter is not the same as a glider: a glider relies on aerodynamic lift without powered flapping, while an ornithopter generates lift through oscillating wings. Leonardo also drew a separate screw-shaped aerial machine, sometimes compared with a helicopter, but that was a different concept.
No Leonardo ornithopter is known to have flown. His work is important because it connected direct observation of birds with systematic studies of aerodynamics and mechanical transmission.