Because I have a lot of time after my retirement for those interests I did not have time during my professional career, I detected the books and lectures by Leonard Susskind, Stanford University, and later the lectures by Alex Flournoy, Colorado School of Mines. I liked both styles of introducing physics, but they are complementary, and therefore I think it is best to enjoy both of them. If, however, both taught the same topic I suggest to watch the lectures by Alex Flournoy first because he explains not only clearly how things are done but also why they are done this way and where students usually have difficulties. One can understand the lectures by Leonard Susskind afterwards much better. The lectures by Alex Flournoy have a clearer structure than the ones by Leonard Susskind, a fact that may come, at least partially, from the different audiences. Leonard Susskind sometimes meanders more through the different topics than following a linearly structured script. I learned most from these two teachers but detected later some other valuable sources.