Socrates

Socrates was an Athenian, the son of a stonemason and a midwife. He served bravely as a foot soldier in the Peloponnesian War, but he spent most of his life in the streets and marketplace of Athens, talking with anyone who would talk with him. He wrote nothing himself; what we know comes mostly from his students Plato and Xenophon and from the comic playwright Aristophanes, who mocked him. Socrates questioned people who claimed to know what courage, justice or piety were, and showed through a series of questions that their answers did not hold together. He said that his only wisdom was knowing that he did not know, and that the unexamined life is not worth living for a human being. Many young men admired him; many powerful citizens resented him. In 399 BC he was tried for not honoring the city's gods and for corrupting the youth, and was condemned to death. He refused to escape and died by drinking hemlock, talking calmly with his friends to the end.

Faith: Practiced Athenian religion but was tried for impiety; his critique reshaped religious thought. Source: Wikipedia