This is the Demosthenes you're probably thinking about. For starters, the name is pronounced Dee-moss-sta-kness, and he lived from 384-322 BC in the happening burg of Athens, Greece.
Ancient D-mo led a large and full life and was called, among other things, "the perfect orator who lacked nothing," "the standard of oratory", and "he stands alone among all the orators."
The full rundown of Demosthenes' life can take a lot of time to go over, so here are the most notable highlights:
Yes, Demosthenes spoke with peebles in his mouth to overcome a speech impediment, namely stuttering. He also spoke over the sounds of the crashing waves to improve his overall speech as well.
As you might have surmised from the quotes above, Ancient D-mo was the most famous and popular orator in ancient Greece.
Ancient D-mo vigorously advocated taking action against King Philip of Macedonia and their encroachment into Greek territories. When Alexander the Great took over, Demosthenes still supported resistance, even though no one listened to him until it was too late.
Demosthenes' most notable speech was entitled "On the Crown." It was actually his defense speech when Aeschines brought trumped-up charges against Demosthenes. As a testament to his popularity at the time, Demosthenes delivered this speech in front of "large" crowd about 1500 Athenians, practically unheard of back in the day. Demosthenes was acquitted of all charges by more than a 4/5 majority.
Sadly, he committed suicide by poisoning himself with the ink of a quill. The Macedonians were hunting down Demosthenes, even after Alexander's death. Demosthenes took refuge in the sanctuary of Poseidon at Calauria; but when the Macedonian soldiers refused to honor that, Ancient D-mo took the "long nap."
If you were to translate the name from Greek into English, Demosthenes = People's Strength.
For a wonderful web page with loads o' detail, and the full run down of Demosthenes' life, punch up...
And of course, Wikipedia has a good article on Ancient D-mo at...