Sir George Cayley
1773-1857
Who
English baronet - "the father of aviation" - who defined the modern fixed-wing aircraft a century before anyone flew in one, and built the first glider reliably reported to carry a human aloft.
Why it matters
Around 1799 Cayley engraved the problem of flight on a silver monogram: lift, weight, drag and thrust, separated for the first time. Everyone before him had copied birds and flapped; Cayley saw that a wing is a surface, not a limb - get the shape and area right, supply the power separately, control it in the air. His 1853 glider flew a man (his coachman, who jumped off at the end and objected to being blamed). He also invented the tensioned wire wheel - bicycles and early aircraft landing gear descend from his workshop. And he published his failures as freely as his successes, which is why his name survived while most rivals' did not.
Lineage
Took the question from the Montgolfiers' balloons, framed it as the four forces - and every aircraft since, plus every lifting body re-entering atmosphere, lives inside that frame. Lilienthal and the Wright brothers built the answer he specified.