The Trial of Socrates
It's the most famous use of hemlock in history. In 399 B.C.E., Socrates — the father of Greek philosophy — was put on trial for impiety and corrupting the youth of Athens. At the time, Socrates was a controversial figure in the city and not particularly liked. He challenged anyone's thinking through his endless and circular Socratic dialogues, and he publicly questioned the gods Athenians worshiped at the time. The only "works" of Socrates survive through the pen of his student Plato, as well as Xenophon. According to those accounts, Socrates supposedly could have escaped Athens after he was found guilty by an Athenian jury. Instead, he chose to stay on principle. He would abide by the law and apparently didn't even try to convince the jury he was innocent. Socrates performed his own execution by drinking hemlock poison.