Short answers, pulled from the story.
Demosthenes died on the 12th of October 322 BC by taking poison that he had concealed in a reed, pretending he wanted to write a letter to his family. He was on the island of Kalaureia, modern-day Poros, having taken sanctuary there after being condemned to death by the Athenian Assembly under pressure from Antipater, Alexander's successor.
On the Crown, delivered in 330 BC, is widely regarded as Demosthenes's masterpiece. He gave the speech to defend the orator Ctesiphon, who had proposed that Athens honour Demosthenes with a golden crown, against a prosecution by his rival Aeschines. Demosthenes won so decisively that Aeschines left Athens permanently.
Demosthenes likely suffered from rhotacism, a condition in which the r sound is mispronounced as l. Plutarch also describes a shortness of breath that broke and disjointed his sentences. He overcame these difficulties through an intensive self-training programme that included speaking with pebbles in his mouth, reciting verses while running or out of breath, and practising in front of a large mirror.
The Philippics were a series of orations delivered by Demosthenes warning Athens about the military and political threat posed by Philip II of Macedon. The First Philippic was delivered around 351-350 BC, and Demosthenes continued to address the same issue in all his speeches until 341 BC. The Third Philippic, delivered in 342 BC, is considered the finest of his political orations.
In 324 BC, Harpalus, who had absconded with treasures entrusted to him by Alexander the Great, sought refuge in Athens. Demosthenes presided over a committee to safeguard Harpalus's money, but when the funds were counted they found only half of what Harpalus had declared. After Harpalus escaped, the Areopagus charged Demosthenes with mishandling twenty talents. He was tried before a jury of 1,500, found guilty, and fined fifty talents, then went into exile.
Quintilian called Demosthenes the standard of oratory, and Cicero described him as the perfect orator who lacked nothing. Longinus compared him to a blazing thunderbolt. During the Middle Ages and Renaissance he was read more than any other ancient orator, and he influenced the authors of The Federalist Papers, major orators of the French Revolution, and Friedrich Nietzsche, who composed sentences according to Demosthenes's stylistic paradigms.