Great ideas have great value iff they are generously and efficiently communicated!
The simultaneously least and most charismatic speaker I have seen is professor Patrick Winston from MIT. Some time ago I watched his great lectures on AI, just for fun. In 2019 a recent iteration of his now classical MIT talk how to speak was made public on YouTube.
The computer scientist at Microsoft Research, professor Simon Peyton Jones, gives a great talk about giving great talks.
How to Give a Great Research Talk
Chris Anderson shares his secrets to the famous TED talk.