Mr. Khan calls his collection of videos "Khan Academy," and he lists himself as founder and faculty. That means he teaches every subject, and he has produced 1,400 lectures since he started in 2006. Now he records one to five lectures per day.
He started with subject matter he knows best—math and engineering, which he studied as an undergraduate at MIT. But lately he has added history lectures about the French Revolution and biology lectures on "Embryonic Stem Cells" and "Introduction to Cellular Respiration."
His site is here.