What prominent Greek orator overcame a speech handicap by putting stones in his mouth?

Demosthenes was a Greek statesman and orator of ancient Athens. His orations constitute a significant expression of contemporary Athenian intellectual prowess and provide an insight into the politics and culture of ancient Greece during the 4th century BC. Demosthenes learned rhetoric by studying the speeches of previous great orators. He delivered his first judicial speeches at the age of 20, in which he argued effectively to gain from his guardians what was left of his inheritance.

Demosthenes started to learn rhetoric because he wished to take his guardians to court and because he was of "delicate physique" and couldn't receive gymnastic education which was customary. In "Parallel Lives" Plutarch states that Demosthenes built an underground study where he practiced speaking and shaving one half of his head so that he could not go out in public. Plutarch also states that he had “an inarticulate and stammering pronunciation” that he got rid of by speaking with pebbles in his mouth and by repeating verses when running or out of breath. He also practiced speaking in front of a large mirror.