Happy birthday, Johann Bernoulli!
Johnann is one of the eight math whizzes of the Bernoullis, a Swiss family that somehow kept birthing amazing mathematicians into the world over a few generations.
This particular Bernoulli spent a lot of his time studying (and teaching!) infinitesimal calculus way back when calculus was at its very beginnings. He tutored both L’Hopital and Euler in math and was specifically thanked in the very first calculus textbook (written by L’Hopital). He also worked with his brother Jakob on a lot of problems, though there was a good deal of friction and the two often fought.
Johann is extra badass, though, because he was a good friend of LEIBNIZ and a student of his calculus. He was also one of the few who took Leibniz’ side and defended him when the whole Newton-Leibniz calculus controversy began. He actually took several problems and showed that they could be solved using Leibniz’ methods, but not Newton’s. A pretty cool guy, if you ask me.