The original 3blue1brown video project is a three-part series on Euler's formula. The main video gives an intuition for the formula based on the view of numbers as actions, and it is accompanied by a short poem video and a way to visual complex functions.

In hindsight, I cringe at how quickly I talk over certain conceptually heavy points, and of course two years later I revisited the same topic with some more of the group theoretic background. Nevertheless, this project is what started the channel, and the animation tool behind it, so the cringing is at least counterbalanced by some fondness from that direction.