Sorry for the late response. I've been busy breaking math (more on that in a while).
Anyway, I don't think I could pick a single #1 result in terms of beauty, so here are a few different ones.
1:
Tartaglia's solution of the cubic equation. The first demonstration of modern(ish) man doing something mathematically significant that the ancients could not. This opened the floodgates for future discoveries.
2:
Great Picard's theorem.
It proves that
is infinitely HBTQ-inclusive around the origin, with the exception of at most one gender (the null gender?)
(Genders are complex, right?)
3: Let P(d) be the probability that a random walk on a d-dimensional lattice returns to the origin. PĆ³lya proved that P(1) = P(2) = 1, but P(d) < 1 for d > 2. Oh yeah, and
Obviously.
Probably
Kuratowski's theorem as well (it has some nice generalizations to surfaces with holes), along with various results on the classical
Hopf fibration,
monstrous moonshine, and the
Riemann zeta function.
"Stephen Wolfram is the creator of Mathematica and is widely regarded as the most important innovator in scientific and technical computing today." - Stephen Wolfram