Sourced
The unexamined life is not worth living.
Source: Apology 38a — spoken by Socrates at his trial
Authors / Plato
Plato wrote dialogues, so most of his famous lines are spoken by Socrates or other characters. That makes him easy to misquote — and two of the most popular "Plato quotes" online belong to a 20th-century philosopher and a Scottish minister.