The story of its original proof fascinates me. Squish together two infinitely non-repeating, irrational, transcendental numbers and an imaginary idea in the correct way and they equal -1. Then slowly prove it over decades by calculating the sine and cosine of the theta angle of thousands of triangles on an x/y plane and realize they are getting closer to your result. Then make the leap to infinity and realize the infinitesimal difference between your answer and -1 can be ignored. I can watch this being done in seconds on YouTube. Euler took a little longer. That level of obstinate, compulsive focus is hard to believe but an impulse I definitely understand. So now I’m getting a masters degree because I was transfixed by this formula. I tattooed it on my right forearm so it is never out of sight.