Joseph-Louis Lagrange (1736–1813) was born in Turin, Italy, with the very Italian name Giuseppe Lodovico Lagrangia — and somehow ended up as France's favourite mathematician. Italian birth certificate, French fan club. Iconic.

His everyday gift to you is tiny but everywhere: the little tick marks. Every single time you write f'(x) or y' for a derivative, that prime is Lagrange's idea. It's the tidiest of all the notations — no fractions to write like Leibniz, no mystery dots like Newton. Just a neat little '.

Physics without the arrows

Lagrange rewrote all of mechanics so smoothly that you can solve "how does this thing move?" problems without drawing a single force arrow — you just track energy and let the maths do the rest. This trick, Lagrangian mechanics, is still how physicists (and the people who build video-game physics engines) do it today. It's F = ma with a glow-up.

He found the best parking spots in space

Lagrange worked out special points where the pull of two big objects (say the Sun and the Earth) balances so perfectly that a smaller thing can just… sit there. We call them Lagrange points, and they are prime real estate: the James Webb Space Telescope is parked at one right now, a million miles from home. There is a literal space telescope floating on Lagrange's homework.

He was such a legend that the Emperor Napoleon personally called him "the lofty pyramid of the mathematical sciences" — which is a very fancy way of saying this guy's a GOAT. He also helped invent the metric system, so every centimetre is partly his fault.

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The full story (with far fewer jokes) is on Wikipedia: Joseph-Louis Lagrange — Wikipedia.