I read this decades ago (another one, yes).

Probably Asimov's or Ray Bradbury's. It's a short tale, some influential people need to lead the general crowd, but unable to do so. They find a man with an outstanding authoritative figure, but he's a dumb man, emotionless, can't speak properly to the crowd, and is a man with no true self personality, no soul. So they prepare speech scripts, with intonation and emotion hint marks, and teach him how to read in front of a large crowd.

The experiment goes very well, and he manages to read perfectly and follow the scripts and the crowds are highly motivated by him.

Bu then, he starts to acquire the taste, and starts performing his own inflections and starts to speak out his own mind to the crowds. He then becomes a fierce dictator and acquires controls of the whole country.

Does anyone remembers which tale is this? Also, is this based on real-world speech techiniques?