3 Blue 1 Brown, it’s a mathematics channel with, as far as I’m concerned, unparalleled production quality.
He’s a Stanford Mathematician who covers everything in topics from topology, number theory, calculus with nothing required beyond High School/1st year undergraduate maths.
Also, his visualisations are nothing short of beautiful.
The python programs he wrote to produce those visualizations is also hosted on GitHub[0]. The repo includes the source for all his videos.