I've had great physics teachers that made me interested in a lot of things, many things not even related to the stuff we actually had to learn.
Also a great math teacher that could always explain things easily and even make jokes, so it was never boring.
It all depends on the person, whether it's the teacher that is supposed to inspire students and make them interested, or a career scientist that still needs to find passion and fun in his work. I personally find all famous scientists, inventors and astronauts that I've seen very interesting and they always showed great passion for their work.
You can also find mathematicians on youtube that deal with math problems and paradoxes in a fun and entertaining way.