Answer: Richard Feynman delivering the first of his famous six lectures on the foundations of physics.

http://research.microsoft.com/apps/tools/tuva/#data=4%7C6b89dded-3eb8-4fa4-bbcd-7c69fe78ed0c%7C%7C

Check it out and see what you think. Feynman sounds enthusiastic, authoritative, articulate, funny, and confident. He also smiles a lot and uses expansive gestures and comes across as a friendly, likeable guy.  His charismatic style is certainly worth studying and emulating.