Thomas Simpson (1710–1761) was an English mathematician who started life as a weaver and taught himself maths from borrowed books. He rose to become a respected teacher and author — living proof that you don't need a grand education to do beautiful work.
Simpson's rule is a small marvel of practical calculus: to estimate the area under a curve, don't
bother with fiddly exact
Two nice twists. First, the "Simpson's rule" story is a bit unfair: the parabola trick was known to others before him, including Newton — Simpson just explained and popularised it so well that his name stuck. Second, his early life reads like an adventure: a run-in over teaching astrology in his home town supposedly forced him to flee, and he ended up scraping a living as a weaver by day and a maths tutor by night before his talent carried him to London. Not bad for a self-taught weaver.