What are some of your favorite videos that explain deep topics in depth?

I've recently been on a 3blue1brown binge (youtube) and am looking for more videos of that ilk. Doesn't have to be a series or a consistent uploader, one off videos are sometimes the best. Just thought I'd ask ~comp if there's anything in particular that comes to mind.

This is in part inspired by the video posted by /u/Deimos in the Technical Goals section of Tildes, titled Simplicity Matters